Bug 898828. Don't even try async video on Windows. r=nical

dom/ipc/ContentParent.cpp

@@ -96,6 +96,7 @@
 #include "nsIWebBrowserChrome.h"
 #include "nsIDocShell.h"
 #include "mozilla/net/NeckoMessageUtils.h"
+#include "gfxPlatform.h"
 
 #if defined(ANDROID) || defined(LINUX)
 #include "nsSystemInfo.h"
@@ -1385,7 +1386,7 @@ ContentParent::InitInternal(ProcessPriority aInitialPriority,
             DebugOnly<bool> opened = PCompositor::Open(this);
             MOZ_ASSERT(opened);
 
-            if (Preferences::GetBool("layers.async-video.enabled",false)) {
+            if (gfxPlatform::AsyncVideoEnabled()) {
                 opened = PImageBridge::Open(this);
                 MOZ_ASSERT(opened);
             }

gfx/thebes/gfxPlatform.cpp

@@ -415,7 +415,7 @@ gfxPlatform::Init()
 
     if (useOffMainThreadCompositing && (XRE_GetProcessType() == GeckoProcessType_Default)) {
         CompositorParent::StartUp();
-        if (Preferences::GetBool("layers.async-video.enabled", false)) {
+        if (AsyncVideoEnabled()) {
             ImageBridgeChild::StartUp();
         }
     }
@@ -2222,3 +2222,13 @@ gfxPlatform::ComponentAlphaEnabled()
   InitLayersAccelerationPrefs();
   return sComponentAlphaEnabled;
 }
+
+bool
+gfxPlatform::AsyncVideoEnabled()
+{
+#ifdef XP_WIN
+  return false;
+#else
+  return Preferences::GetBool("layers.async-video.enabled", false);
+#endif
+}

gfx/thebes/gfxPlatform.h

@@ -519,6 +519,10 @@ public:
 
     static bool ComponentAlphaEnabled();
 
+    // Async video is enabled on this platform.
+    // Must only be called from the main thread.
+    static bool AsyncVideoEnabled();
+
     /**
      * Are we going to try color management?
      */

modules/libpref/src/init/all.js

@@ -4102,9 +4102,12 @@ pref("layers.scroll-graph", false);
 pref("layers.offmainthreadcomposition.enabled", false);
 // Whether to use the deprecated texture architecture rather than the new one.
 pref("layers.use-deprecated-textures", true);
+#ifndef XP_WIN
 // Asynchonous video compositing using the ImageBridge IPDL protocol.
 // requires off-main-thread compositing.
+// Never works on Windows, so no point pref'ing it on.
 pref("layers.async-video.enabled",false);
+#endif
 
 #ifdef XP_MACOSX
 pref("layers.offmainthreadcomposition.enabled", true);