Bug 1345142. Move Image discard back to child. r=nical

This gets rid of the implicit discard that happens on the parent side
when using external images.

gfx/layers/wr/WebRenderBridgeParent.cpp

@@ -343,8 +343,6 @@ WebRenderBridgeParent::ProcessWebRenderCommands(const gfx::IntSize &aSize,
                                                 const ByteBuffer& aux,
                                                 const WrAuxiliaryListsDescriptor& auxDesc)
 {
-  // XXX remove it when external image key is used.
-  std::vector<wr::ImageKey> keysToDelete;
 
   for (InfallibleTArray<WebRenderParentCommand>::index_type i = 0; i < aCommands.Length(); ++i) {
     const WebRenderParentCommand& cmd = aCommands[i];
@@ -375,7 +373,6 @@ WebRenderBridgeParent::ProcessWebRenderCommands(const gfx::IntSize &aSize,
                                          descriptor,
                                          wrTexture->GetExternalImageKey());
             mCompositableHolder->HoldExternalImage(mPipelineId, aEpoch, texture->AsWebRenderTextureHost());
-            keysToDelete.push_back(key);
           } else {
             // XXX handling YUV
             gfx::SurfaceFormat format =
@@ -385,7 +382,6 @@ WebRenderBridgeParent::ProcessWebRenderCommands(const gfx::IntSize &aSize,
                                          descriptor,
                                          wrTexture->GetExternalImageKey());
             mCompositableHolder->HoldExternalImage(mPipelineId, aEpoch, texture->AsWebRenderTextureHost());
-            keysToDelete.push_back(key);
           }
 
           break;
@@ -405,7 +401,6 @@ WebRenderBridgeParent::ProcessWebRenderCommands(const gfx::IntSize &aSize,
         auto slice = Range<uint8_t>(map.mData, size.height * map.mStride);
         mApi->AddImage(key, descriptor, slice);
 
-        keysToDelete.push_back(key);
         dSurf->Unmap();
         break;
       }
@@ -433,11 +428,6 @@ WebRenderBridgeParent::ProcessWebRenderCommands(const gfx::IntSize &aSize,
   ScheduleComposition();
   DeleteOldImages();
 
-  // XXX remove it when external image key is used.
-  if (!keysToDelete.empty()) {
-    mKeysToDelete.swap(keysToDelete);
-  }
-
   if (ShouldParentObserveEpoch()) {
     mCompositorBridge->ObserveLayerUpdate(wr::AsUint64(mPipelineId), GetChildLayerObserverEpoch(), true);
   }

gfx/layers/wr/WebRenderCanvasLayer.cpp

@@ -83,6 +83,7 @@ WebRenderCanvasLayer::RenderLayer(wr::DisplayListBuilder& aBuilder)
   key.mNamespace = WrBridge()->GetNamespace();
   key.mHandle = WrBridge()->GetNextResourceId();
   WrBridge()->AddWebRenderParentCommand(OpAddExternalImage(mExternalImageId, key));
+  Manager()->AddImageKeyForDiscard(key);
 
   aBuilder.PushStackingContext(wr::ToWrRect(relBounds),
                                1.0f,

gfx/layers/wr/WebRenderImageLayer.cpp

@@ -211,6 +211,7 @@ WebRenderImageLayer::RenderMaskLayer(const gfx::Matrix4x4& aTransform)
   key.mNamespace = WrBridge()->GetNamespace();
   key.mHandle = WrBridge()->GetNextResourceId();
   WrBridge()->AddWebRenderParentCommand(OpAddExternalImage(mExternalImageId, key));
+  Manager()->AddImageKeyForDiscard(key);
 
   gfx::IntSize size = image->GetSize();
   WrImageMask imageMask;

gfx/layers/wr/WebRenderPaintedLayer.cpp

@@ -208,6 +208,7 @@ WebRenderPaintedLayer::RenderLayer(wr::DisplayListBuilder& aBuilder)
                               mixBlendMode);
   aBuilder.PushImage(wr::ToWrRect(rect), clip, wr::ImageRendering::Auto, key);
   aBuilder.PopStackingContext();
+  Manager()->AddImageKeyForDiscard(key);
 }
 
 } // namespace layers