Bug 962041 - Fix component apha with the new ContentClient/Host. r=mattwoodrow

gfx/layers/client/ContentClient.cpp

@@ -281,6 +281,9 @@ ContentClientRemoteBuffer::Updated(const nsIntRegion& aRegionToDraw,
 
   MOZ_ASSERT(mTextureClient);
   mForwarder->UseTexture(this, mTextureClient);
+  if (mTextureClientOnWhite) {
+    mForwarder->UseTexture(this, mTextureClientOnWhite);
+  }
   mForwarder->UpdateTextureRegion(this,
                                   ThebesBufferData(BufferRect(),
                                                    BufferRotation()),

gfx/layers/composite/ContentHost.cpp

@@ -127,7 +127,7 @@ ContentHostBase::Composite(EffectChain& aEffectChain,
     tileIter->BeginTileIteration();
   }
 
-  if (mTextureHostOnWhite) {
+  if (sourceOnWhite) {
     iterOnWhite = sourceOnWhite->AsTileIterator();
     MOZ_ASSERT(!tileIter || tileIter->GetTileCount() == iterOnWhite->GetTileCount(),
                "Tile count mismatch on component alpha texture");
@@ -221,11 +221,9 @@ void
 ContentHostBase::UseTextureHost(TextureHost* aTexture)
 {
   if (aTexture->GetFlags() & TEXTURE_ON_WHITE) {
-    mTextureHost = nullptr;
     mTextureHostOnWhite = aTexture;
     mTextureHostOnWhite->SetCompositor(GetCompositor());
   } else {
-    mTextureHostOnWhite = nullptr;
     mTextureHost = aTexture;
     mTextureHost->SetCompositor(GetCompositor());
   }