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 ea5772480c321aaa0cc6146331827bcf56d675cf..afb67c4380e430f5e63b12c5f705463fa3167ceb 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 canceled 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
@@ -195,6 +221,9 @@ class COMPOSITOR_EXPORT Compositor
   // (i.e. |Compositor::Initialize(true)| was called).
   bool IsThreaded() const;
 
+  // Creates a compositor lock.
+  scoped_refptr<CompositorLock> GetCompositorLock();
+
   // Internal functions, called back by command-buffer contexts on swap buffer
   // events.
 
@@ -224,6 +253,10 @@ class COMPOSITOR_EXPORT Compositor
 
  private:
   friend class base::RefCounted<Compositor>;
+  friend class CompositorLock;
+
+  // Called by CompositorLock.
+  void Unlock();
 
   // When reading back pixel data we often get RGBA rather than BGRA pixels and
   // and the image often needs to be flipped vertically.
@@ -258,6 +291,21 @@ class COMPOSITOR_EXPORT Compositor
 
   bool disable_schedule_composite_;
 
+  enum CommitsAllowedState {
+    // We've told |root_layer_| to enable commits, but no commit has cleared.
+    ENABLED_NEEDS_COMMIT,
+    // We've committed since being enabled.
+    ENABLED_DID_COMMIT,
+    // We will tell |root_layer_| to defer commits once an commit clears.
+    DISABLED_PENDING_COMMIT,
+    // We told |root_layer_| to disable commits.
+    DISABLED,
+  };
+
+  CommitsAllowedState commits_allowed_;
+
+  CompositorLock* compositor_lock_;
+
   DISALLOW_COPY_AND_ASSIGN(Compositor);
 };