Bug 1567319 - Discard payloads for no-op composites. r=bas

Differential Revision: https://phabricator.services.mozilla.com/D40569

--HG--
extra : moz-landing-system : lando

gfx/layers/composite/LayerManagerComposite.cpp

@@ -592,6 +592,12 @@ void LayerManagerComposite::UpdateAndRender() {
     // Composition requested, but nothing has changed. Don't do any work.
     mClonedLayerTreeProperties = LayerProperties::CloneFrom(GetRoot());
     mProfilerScreenshotGrabber.NotifyEmptyFrame();
+
+    // Discard the current payloads. These payloads did not require a composite
+    // (they caused no changes to anything visible), so we don't want to measure
+    // their latency.
+    mPayload.Clear();
+
     return;
   }
 
@@ -987,6 +993,12 @@ bool LayerManagerComposite::Render(const nsIntRegion& aInvalidRegion,
   if (actualBounds.IsEmpty()) {
     mProfilerScreenshotGrabber.NotifyEmptyFrame();
     mCompositor->GetWidget()->PostRender(&widgetContext);
+
+    // Discard the current payloads. These payloads did not require a composite
+    // (they caused no changes to anything visible), so we don't want to measure
+    // their latency.
+    mPayload.Clear();
+
     return true;
   }
 

gfx/layers/mlgpu/LayerManagerMLGPU.cpp

@@ -313,6 +313,12 @@ void LayerManagerMLGPU::Composite() {
   if (!mSwapChain->ApplyNewInvalidRegion(std::move(mInvalidRegion),
                                          diagnosticRect)) {
     mProfilerScreenshotGrabber.NotifyEmptyFrame();
+
+    // Discard the current payloads. These payloads did not require a composite
+    // (they caused no changes to anything visible), so we don't want to measure
+    // their latency.
+    mPayload.Clear();
+
     return;
   }