cc/blimp: Add synchronization for scroll/scale state.

blimp/client/core/compositor/blimp_compositor.h

Index: blimp/client/core/compositor/blimp_compositor.h
diff --git a/blimp/client/core/compositor/blimp_compositor.h b/blimp/client/core/compositor/blimp_compositor.h
index cf14c64cfae17b9ba522bb774b7ffebf771c1e44..8d80311b98f489b587bebe112078ae47d3ca9c58 100644
--- a/blimp/client/core/compositor/blimp_compositor.h
+++ b/blimp/client/core/compositor/blimp_compositor.h
@@ -13,7 +13,7 @@
 #include "base/threading/thread_checker.h"
 #include "blimp/client/core/compositor/blimp_compositor_frame_sink_proxy.h"
 #include "blimp/client/public/compositor/compositor_dependencies.h"
-#include "cc/blimp/compositor_state_deserializer_client.h"
+#include "cc/blimp/compositor_state_deserializer.h"
 #include "cc/surfaces/surface_factory_client.h"
 #include "cc/trees/layer_tree_host.h"
 #include "cc/trees/layer_tree_host_client.h"
@@ -34,10 +34,9 @@ namespace proto {
 class CompositorMessage;
 }  // namespace proto
 
-class CompositorStateDeserializer;
 class ContextProvider;
 class Layer;
-class LayerTreeHost;
+class LayerTreeHostInProcess;
 class LayerTreeSettings;
 class LocalFrameid;
 class Surface;
@@ -120,7 +119,7 @@ class BlimpCompositor : public cc::LayerTreeHostClient,
                            const gfx::Vector2dF& outer_delta,
                            const gfx::Vector2dF& elastic_overscroll_delta,
                            float page_scale,
-                           float top_controls_delta) override {}
+                           float top_controls_delta) override;
   void RequestNewCompositorFrameSink() override;
   void DidInitializeCompositorFrameSink() override;
   // TODO(khushalsagar): Need to handle context initialization failures.
@@ -146,9 +145,7 @@ class BlimpCompositor : public cc::LayerTreeHostClient,
   void SetBeginFrameSource(cc::BeginFrameSource* begin_frame_source) override {}
 
   // CompositorStateDeserializerClient implementation.
-  bool ShouldRetainClientScroll(int engine_layer_id,
-                                const gfx::ScrollOffset& new_offset) override;
-  bool ShouldRetainClientPageScale(float new_page_scale) override;
+  void DidUpdateLocalState() override;
 
   void HandleCompositorMessageToImpl(
       std::unique_ptr<cc::proto::CompositorMessage> message);
@@ -185,9 +182,9 @@ class BlimpCompositor : public cc::LayerTreeHostClient,
   // frame should be started.
   void SubmitCompositorFrameAck();
 
-  // Called when the local copy of the layer with |engine_layer_id| on the
-  // engine was scrolled on the compositor thread.
-  void LayerScrolled(int engine_layer_id);
+  // Sends an update to the engine if the state on the client was modified and
+  // an ack for a previous update sent is not pending.
+  void FlushClientState();
 
   // Set to true if we are using a LayerTreeHostInProcess to process frame
   // updates from the engine.
@@ -199,7 +196,7 @@ class BlimpCompositor : public cc::LayerTreeHostClient,
 
   cc::FrameSinkId frame_sink_id_;
 
-  std::unique_ptr<cc::LayerTreeHost> host_;
+  std::unique_ptr<cc::LayerTreeHostInProcess> host_;
 
   // The SurfaceFactory is bound to the lifetime of the |proxy_client_|. When
   // detached, the surface factory will be destroyed.
@@ -245,6 +242,14 @@ class BlimpCompositor : public cc::LayerTreeHostClient,
   std::unique_ptr<cc::CompositorStateDeserializer>
       compositor_state_deserializer_;
 
+  // Set to true if the compositor state on the client was modified on the impl
+  // thread and an update needs to be sent to the engine.
+  bool client_state_dirty_ = false;
+
+  // Set to true if a client state update was sent to the engine and an ack for
+  // this update from the engine is pending.
+  bool client_state_update_ack_pending_ = false;
+
   base::WeakPtrFactory<BlimpCompositor> weak_ptr_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(BlimpCompositor);