Aura: Resize locks with --ui-enable-threaded-compositing

ui/compositor/compositor.h

Index: ui/compositor/compositor.h
diff --git a/ui/compositor/compositor.h b/ui/compositor/compositor.h
index c5dc3ba076a19d948fe0e2a811291ea65d0cd9d9..f3720bce3cd7a3b81c6e9ceb54bfb3c71720eb16 100644
--- a/ui/compositor/compositor.h
+++ b/ui/compositor/compositor.h
@@ -126,6 +126,32 @@ class COMPOSITOR_EXPORT CompositorDelegate {
   virtual ~CompositorDelegate() {}
 };
 
+// This class represents a lock on the compositor, that can be used to prevent
+// commits to the compositor tree while we're waiting for an asynchronous
+// event. The typical use case is when waiting for a renderer to produce a frame
+// at the right size. The caller keeps a reference on this object, and drops the
+// reference once it desires to release the lock.
+// Note however that the lock is cancelled after a short timeout to ensure
+// responsiveness of the UI, so the compositor tree should be kept in a
+// "reasonable" state while the lock is held.
+// Don't instantiate this class directly, use Compositor::GetCompositorLock.
+class COMPOSITOR_EXPORT CompositorLock
+    : public base::RefCounted<CompositorLock>,
+      public base::SupportsWeakPtr<CompositorLock> {
+ private:
+  friend class base::RefCounted<CompositorLock>;
+  friend class Compositor;
+
+  explicit CompositorLock(Compositor* compositor);
+  ~CompositorLock();
+
+  void CancelLock();
+
+  Compositor* compositor_;
+  DISALLOW_COPY_AND_ASSIGN(CompositorLock);
+};
+
+
 // Compositor object to take care of GPU painting.
 // A Browser compositor object is responsible for generating the final
 // displayable form of pixels comprising a single widget's contents. It draws an
@@ -196,9 +222,9 @@ class COMPOSITOR_EXPORT Compositor
   // and the OnCompositingEnded.
   bool DrawPending() const { return swap_posted_; }
 
-  // Returns whether the drawing is issued from a separate thread
-  // (i.e. |Compositor::Initialize(true)| was called).
-  bool IsThreaded() const;
+  // Creates a compositor lock. Returns NULL if it is not possible to lock at
+  // this time (i.e. we're waiting to complete a previous unlock).
+  scoped_refptr<CompositorLock> GetCompositorLock();
 
   // Internal functions, called back by command-buffer contexts on swap buffer
   // events.
@@ -227,8 +253,17 @@ class COMPOSITOR_EXPORT Compositor
   int last_started_frame() { return last_started_frame_; }
   int last_ended_frame() { return last_ended_frame_; }
 
+  bool IsLocked() { return compositor_lock_ != NULL; }
+
  private:
   friend class base::RefCounted<Compositor>;
+  friend class CompositorLock;
+
+  // Called by CompositorLock.
+  void UnlockCompositor();
+
+  // Called to release any pending CompositorLock
+  void CancelCompositorLock();
 
   // Notifies the compositor that compositing is complete.
   void NotifyEnd();
@@ -258,6 +293,8 @@ class COMPOSITOR_EXPORT Compositor
 
   bool disable_schedule_composite_;
 
+  CompositorLock* compositor_lock_;
+
   DISALLOW_COPY_AND_ASSIGN(Compositor);
 };