Backed out changeset ea2341b06e6f (bug 994541) for reftest timeouts

modules/libpref/src/init/all.js

@@ -3832,7 +3832,7 @@ pref("layers.max-active", -1);
 pref("layers.scroll-graph", false);
 
 // Set the default values, and then override per-platform as needed
-pref("layers.offmainthreadcomposition.enabled", true);
+pref("layers.offmainthreadcomposition.enabled", false);
 // Compositor target frame rate. NOTE: If vsync is enabled the compositor
 // frame rate will still be capped.
 // -1 -> default (match layout.frame_rate or 60 FPS)
@@ -3845,14 +3845,31 @@ pref("layers.async-video.enabled", true);
 pref("layers.async-video-oop.enabled",true);
 
 #ifdef XP_WIN
+pref("layers.offmainthreadcomposition.enabled", true);
 // XXX - see bug 1009616
 pref("layers.async-video-oop.enabled", false);
 #endif
 
+#ifdef MOZ_WIDGET_QT
+pref("layers.offmainthreadcomposition.enabled", true);
+#endif
+
+#ifdef XP_MACOSX
+pref("layers.offmainthreadcomposition.enabled", true);
+#endif
+
+// ANDROID covers android and b2g
+#ifdef ANDROID
+pref("layers.offmainthreadcomposition.enabled", true);
+#endif
+
 // same effect as layers.offmainthreadcomposition.enabled, but specifically for
 // use with tests.
 pref("layers.offmainthreadcomposition.testing.enabled", false);
 
+// whether to allow use of the basic compositor
+pref("layers.offmainthreadcomposition.force-basic", false);
+
 // Whether to animate simple opacity and transforms on the compositor
 pref("layers.offmainthreadcomposition.async-animations", false);
 

widget/xpwidgets/nsBaseWidget.cpp

@@ -872,6 +872,20 @@ nsBaseWidget::GetPreferredCompositorBackends(nsTArray<LayersBackend>& aHints)
   aHints.AppendElement(LayersBackend::LAYERS_BASIC);
 }
 
+static void
+CheckForBasicBackends(nsTArray<LayersBackend>& aHints)
+{
+#ifndef XP_WIN
+  for (size_t i = 0; i < aHints.Length(); ++i) {
+    if (aHints[i] == LayersBackend::LAYERS_BASIC &&
+        !Preferences::GetBool("layers.offmainthreadcomposition.force-basic", false)) {
+      // basic compositor is not stable enough for regular use
+      aHints[i] = LayersBackend::LAYERS_NONE;
+    }
+  }
+#endif
+}
+
 void nsBaseWidget::CreateCompositor(int aWidth, int aHeight)
 {
   MOZ_ASSERT(gfxPlatform::UsesOffMainThreadCompositing(),
@@ -901,6 +915,10 @@ void nsBaseWidget::CreateCompositor(int aWidth, int aHeight)
   nsTArray<LayersBackend> backendHints;
   GetPreferredCompositorBackends(backendHints);
 
+  if (!mRequireOffMainThreadCompositing) {
+    CheckForBasicBackends(backendHints);
+  }
+
   bool success = false;
   if (!backendHints.IsEmpty()) {
     shadowManager = mCompositorChild->SendPLayerTransactionConstructor(