Bug 1061209 - disable basic layers OMTC except on linux and e10s. r=mattwoodrow

widget/xpwidgets/nsBaseWidget.cpp

@@ -872,6 +872,19 @@ nsBaseWidget::GetPreferredCompositorBackends(nsTArray<LayersBackend>& aHints)
   aHints.AppendElement(LayersBackend::LAYERS_BASIC);
 }
 
+static void
+RemoveBasicBackend(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)) {
+      aHints[i] = LayersBackend::LAYERS_NONE;
+    }
+  }
+#endif
+}
+
 void nsBaseWidget::CreateCompositor(int aWidth, int aHeight)
 {
   MOZ_ASSERT(gfxPlatform::UsesOffMainThreadCompositing(),
@@ -901,6 +914,12 @@ void nsBaseWidget::CreateCompositor(int aWidth, int aHeight)
   nsTArray<LayersBackend> backendHints;
   GetPreferredCompositorBackends(backendHints);
 
+#ifndef MOZ_X11
+  if (!mRequireOffMainThreadCompositing) {
+    RemoveBasicBackend(backendHints);
+  }
+#endif
+
   bool success = false;
   if (!backendHints.IsEmpty()) {
     shadowManager = mCompositorChild->SendPLayerTransactionConstructor(