exo: Only create new SurfaceLayer if layer properties change.

components/exo/surface.h

Index: components/exo/surface.h
diff --git a/components/exo/surface.h b/components/exo/surface.h
index 016fe113fd6c175dbcb01257c4cceededf6712ea..0822fe56b0e0a3bf264abd94a4100019cf3ea7e9 100644
--- a/components/exo/surface.h
+++ b/components/exo/surface.h
@@ -219,11 +219,22 @@ class Surface : public aura::Window,
 
   void WillDraw(cc::SurfaceId surface_id);
 
+  // Check whether this Surface and its children need to create new cc::Surface
+  // IDs for their contents next time they get new buffer contents.
+  void CheckForCommittingToNewSurface();
+
  private:
   bool needs_commit_surface_hierarchy() const {
     return needs_commit_surface_hierarchy_;
   }
 
+  // Returns true if any child surface needs a commit and has
+  // modified_layer_info_ true.
+  bool HaveChildLayersChanged();
+
+  // Sets that all children must create new cc::SurfaceIds for their contents.
+  void SetChildrenCommitToNewSurface();
+
   // Commit the current attached buffer to a TextureLayer.
   void CommitTextureContents();
 
@@ -243,6 +254,16 @@ class Surface : public aura::Window,
   // rather than a TextureLayer.
   static bool use_surface_layer_;
 
+  // This is true if it's possible that the layer properties (size, opacity,
+  // etc.) may have been modified since the last commit. Attaching a new
+  // buffer with the same size as the old shouldn't set this to true.
+  bool modified_layer_info_ = true;
+
+  // This is true if the next commit to this surface should put its contents
+  // into a new cc::SurfaceId. This allows for synchronization between Surface
+  // and layer changes.
+  bool commit_to_new_surface_ = true;
+

[reveman, 2016/06/09 14:19:29]

Check my comments in the .cc file but I'm curious to know if this additional
state can't be avoided using some better integration with
CommitSurfaceHierarchy().

   // This is true when Attach() has been called and new contents should take
   // effect next time Commit() is called.
   bool has_pending_contents_;