Bug 939598. Always call BeginTransaction before EndTransaction. r=mattwoodrow

gfx/layers/composite/LayerManagerComposite.cpp

@@ -168,10 +168,11 @@ LayerManagerComposite::BeginTransactionWithDrawTarget(DrawTarget* aTarget)
 bool
 LayerManagerComposite::EndEmptyTransaction(EndTransactionFlags aFlags)
 {
-  mInTransaction = false;
-
-  if (!mRoot)
+  NS_ASSERTION(mInTransaction, "Didn't call BeginTransaction?");
+  if (!mRoot) {
+    mInTransaction = false;
     return false;
+  }
 
   EndTransaction(nullptr, nullptr);
   return true;
@@ -182,6 +183,7 @@ LayerManagerComposite::EndTransaction(DrawThebesLayerCallback aCallback,
                                       void* aCallbackData,
                                       EndTransactionFlags aFlags)
 {
+  NS_ASSERTION(mInTransaction, "Didn't call BeginTransaction?");
   mInTransaction = false;
 
 #ifdef MOZ_LAYERS_HAVE_LOG

gfx/layers/ipc/CompositorParent.cpp

@@ -500,6 +500,15 @@ CompositorParent::ScheduleComposition()
 
 void
 CompositorParent::Composite()
+{
+  if (CanComposite()) {
+    mLayerManager->BeginTransaction();
+  }
+  CompositeInTransaction();
+}
+
+void
+CompositorParent::CompositeInTransaction()
 {
   profiler_tracing("Paint", "Composite", TRACING_INTERVAL_START);
   PROFILER_LABEL("CompositorParent", "Composite");
@@ -564,7 +573,7 @@ CompositorParent::ComposeToTarget(DrawTarget* aTarget)
   mLayerManager->BeginTransactionWithDrawTarget(aTarget);
   // Since CanComposite() is true, Composite() must end the layers txn
   // we opened above.
-  Composite();
+  CompositeInTransaction();
 }
 
 bool
@@ -629,10 +638,7 @@ CompositorParent::ShadowLayersUpdated(LayerTransactionParent* aLayerTree,
     }
   }
   ScheduleComposition();
-  LayerManagerComposite *layerComposite = mLayerManager->AsLayerManagerComposite();
-  if (layerComposite) {
-    layerComposite->NotifyShadowTreeTransaction();
-  }
+  mLayerManager->NotifyShadowTreeTransaction();
 }
 
 void

gfx/layers/ipc/CompositorParent.h

@@ -230,7 +230,8 @@ protected:
                                  bool* aSuccess);
   virtual bool DeallocPLayerTransactionParent(PLayerTransactionParent* aLayers);
   virtual void ScheduleTask(CancelableTask*, int);
-  virtual void Composite();
+  void Composite();
+  void CompositeInTransaction();
   virtual void ComposeToTarget(gfx::DrawTarget* aTarget);
 
   void SetEGLSurfaceSize(int width, int height);