diff --git a/gfx/layers/apz/testutil/APZTestData.h b/gfx/layers/apz/testutil/APZTestData.h
index c6f914bd71e1..009577a31888 100644
--- a/gfx/layers/apz/testutil/APZTestData.h
+++ b/gfx/layers/apz/testutil/APZTestData.h
@@ -13,6 +13,7 @@
 #include "mozilla/Assertions.h"  // for MOZ_ASSERT
 #include "mozilla/DebugOnly.h"   // for DebugOnly
 #include "mozilla/ToString.h"    // for ToString
+#include "ipc/IPCMessageUtils.h"
 
 namespace mozilla {
 namespace layers {
@@ -36,6 +37,7 @@ typedef uint32_t SequenceNumber;
 //    with the sequence number of the paint that caused the layers update.
 class APZTestData {
   typedef FrameMetrics::ViewID ViewID;
+  friend struct IPC::ParamTraits<APZTestData>;
 public:
   void StartNewPaint(SequenceNumber aSequenceNumber) {
     auto insertResult = mPaints.insert(DataStore::value_type(aSequenceNumber, Bucket()));
@@ -131,4 +133,39 @@ private:
 }
 }
 
+namespace IPC {
+
+template <>
+struct ParamTraits<mozilla::layers::APZTestData>
+{
+  typedef mozilla::layers::APZTestData paramType;
+
+  static void Write(Message* aMsg, const paramType& aParam)
+  {
+    WriteParam(aMsg, aParam.mPaints);
+    WriteParam(aMsg, aParam.mRepaintRequests);
+  }
+
+  static bool Read(const Message* aMsg, void** aIter, paramType* aResult)
+  {
+    return (ReadParam(aMsg, aIter, &aResult->mPaints) &&
+            ReadParam(aMsg, aIter, &aResult->mRepaintRequests));
+  }
+};
+
+template <>
+struct ParamTraits<mozilla::layers::APZTestData::ScrollFrameData>
+  : ParamTraits<mozilla::layers::APZTestData::ScrollFrameDataBase> {};
+
+template <>
+struct ParamTraits<mozilla::layers::APZTestData::Bucket>
+  : ParamTraits<mozilla::layers::APZTestData::BucketBase> {};
+
+template <>
+struct ParamTraits<mozilla::layers::APZTestData::DataStore>
+  : ParamTraits<mozilla::layers::APZTestData::DataStoreBase> {};
+
+}
+
+
 #endif /* mozilla_layers_APZTestData_h */
diff --git a/gfx/layers/ipc/CompositorParent.cpp b/gfx/layers/ipc/CompositorParent.cpp
index 88cce32ff8f4..242db232baa9 100644
--- a/gfx/layers/ipc/CompositorParent.cpp
+++ b/gfx/layers/ipc/CompositorParent.cpp
@@ -858,6 +858,14 @@ CompositorParent::RecvRequestOverfill()
   return true;
 }
 
+void
+CompositorParent::GetAPZTestData(const LayerTransactionParent* aLayerTree,
+                                 APZTestData* aOutData)
+{
+  *aOutData = sIndirectLayerTrees[mRootLayerTreeID].mApzTestData;
+}
+
+
 void
 CompositorParent::InitializeLayerManager(const nsTArray<LayersBackend>& aBackendHints)
 {
@@ -1141,6 +1149,8 @@ public:
   virtual bool SetTestSampleTime(LayerTransactionParent* aLayerTree,
                                  const TimeStamp& aTime) MOZ_OVERRIDE;
   virtual void LeaveTestMode(LayerTransactionParent* aLayerTree) MOZ_OVERRIDE;
+  virtual void GetAPZTestData(const LayerTransactionParent* aLayerTree,
+                              APZTestData* aOutData) MOZ_OVERRIDE;
 
   virtual AsyncCompositionManager* GetCompositionManager(LayerTransactionParent* aParent) MOZ_OVERRIDE;
 
@@ -1357,6 +1367,16 @@ CrossProcessCompositorParent::LeaveTestMode(LayerTransactionParent* aLayerTree)
   state->mParent->LeaveTestMode(aLayerTree);
 }
 
+void
+CrossProcessCompositorParent::GetAPZTestData(const LayerTransactionParent* aLayerTree,
+                                             APZTestData* aOutData)
+{
+  uint64_t id = aLayerTree->GetId();
+  MOZ_ASSERT(id != 0);
+  *aOutData = sIndirectLayerTrees[id].mApzTestData;
+}
+
+
 AsyncCompositionManager*
 CrossProcessCompositorParent::GetCompositionManager(LayerTransactionParent* aLayerTree)
 {
diff --git a/gfx/layers/ipc/CompositorParent.h b/gfx/layers/ipc/CompositorParent.h
index 31288eb1c1f0..af7775929f4e 100644
--- a/gfx/layers/ipc/CompositorParent.h
+++ b/gfx/layers/ipc/CompositorParent.h
@@ -104,6 +104,8 @@ public:
   virtual bool SetTestSampleTime(LayerTransactionParent* aLayerTree,
                                  const TimeStamp& aTime) MOZ_OVERRIDE;
   virtual void LeaveTestMode(LayerTransactionParent* aLayerTree) MOZ_OVERRIDE;
+  virtual void GetAPZTestData(const LayerTransactionParent* aLayerTree,
+                              APZTestData* aOutData) MOZ_OVERRIDE;
   virtual AsyncCompositionManager* GetCompositionManager(LayerTransactionParent* aLayerTree) MOZ_OVERRIDE { return mCompositionManager; }
 
   /**
diff --git a/gfx/layers/ipc/LayerTransactionParent.cpp b/gfx/layers/ipc/LayerTransactionParent.cpp
index 60fce36fd070..ce50b3250dc0 100644
--- a/gfx/layers/ipc/LayerTransactionParent.cpp
+++ b/gfx/layers/ipc/LayerTransactionParent.cpp
@@ -693,6 +693,13 @@ LayerTransactionParent::RecvSetAsyncScrollOffset(PLayerParent* aLayer,
   return true;
 }
 
+bool
+LayerTransactionParent::RecvGetAPZTestData(APZTestData* aOutData)
+{
+  mShadowLayersManager->GetAPZTestData(this, aOutData);
+  return true;
+}
+
 bool
 LayerTransactionParent::Attach(ShadowLayerParent* aLayerParent,
                                CompositableHost* aCompositable,
diff --git a/gfx/layers/ipc/LayerTransactionParent.h b/gfx/layers/ipc/LayerTransactionParent.h
index 722e16cfb40f..e52ec4de079d 100644
--- a/gfx/layers/ipc/LayerTransactionParent.h
+++ b/gfx/layers/ipc/LayerTransactionParent.h
@@ -109,6 +109,7 @@ protected:
                                          MOZ_OVERRIDE;
   virtual bool RecvSetAsyncScrollOffset(PLayerParent* aLayer,
                                         const int32_t& aX, const int32_t& aY) MOZ_OVERRIDE;
+  virtual bool RecvGetAPZTestData(APZTestData* aOutData);
 
   virtual PLayerParent* AllocPLayerParent() MOZ_OVERRIDE;
   virtual bool DeallocPLayerParent(PLayerParent* actor) MOZ_OVERRIDE;
diff --git a/gfx/layers/ipc/PLayerTransaction.ipdl b/gfx/layers/ipc/PLayerTransaction.ipdl
index 449e59122239..cd33e03f2bd1 100644
--- a/gfx/layers/ipc/PLayerTransaction.ipdl
+++ b/gfx/layers/ipc/PLayerTransaction.ipdl
@@ -18,6 +18,7 @@ include "mozilla/GfxMessageUtils.h";
 using struct mozilla::layers::TextureInfo from "mozilla/layers/CompositorTypes.h";
 using struct mozilla::void_t from "ipc/IPCMessageUtils.h";
 using mozilla::layers::TextureFlags from "mozilla/layers/CompositorTypes.h";
+using class mozilla::layers::APZTestData from "mozilla/layers/APZTestData.h";
 
 /**
  * The layers protocol is spoken between thread contexts that manage
@@ -89,6 +90,10 @@ parent:
   // Schedule a composite if one isn't already scheduled.
   async ForceComposite();
 
+  // Get a copy of the compositor-side APZ test data instance for this
+  // layers id.
+  sync GetAPZTestData() returns (APZTestData data);
+
   async ChildAsyncMessages(AsyncChildMessageData[] aMessages);
 
   async __delete__();
diff --git a/gfx/layers/ipc/ShadowLayersManager.h b/gfx/layers/ipc/ShadowLayersManager.h
index 7a695908ba19..02fa130966e3 100644
--- a/gfx/layers/ipc/ShadowLayersManager.h
+++ b/gfx/layers/ipc/ShadowLayersManager.h
@@ -13,6 +13,7 @@ namespace layers {
 class TargetConfig;
 class LayerTransactionParent;
 class AsyncCompositionManager;
+class APZTestData;
 
 class ShadowLayersManager
 {
@@ -29,6 +30,8 @@ public:
     virtual bool SetTestSampleTime(LayerTransactionParent* aLayerTree,
                                    const TimeStamp& aTime) { return true; }
     virtual void LeaveTestMode(LayerTransactionParent* aLayerTree) { }
+    virtual void GetAPZTestData(const LayerTransactionParent* aLayerTree,
+                                APZTestData* aOutData) { }
 };
 
 } // layers