cc: Enforce correct recycling in resource pool.

cc/resource_provider.h

Index: cc/resource_provider.h
diff --git a/cc/resource_provider.h b/cc/resource_provider.h
index c4776c21f9f6a89b0023abcaf1fd582786f87cb2..af22a6b18a7bb1336e7e81401b600af4bc0c5b6c 100644
--- a/cc/resource_provider.h
+++ b/cc/resource_provider.h
@@ -221,6 +221,11 @@ public:
         DISALLOW_COPY_AND_ASSIGN(ScopedWriteLockSoftware);
     };
 
+    class Fence : public base::RefCounted<Fence> {
+    public:
+        virtual bool hasPassed() = 0;
+    };
+
     // Acquire pixel buffer for resource. The pixel buffer can be used to
     // set resource pixels without performing unnecessary copying.
     void acquirePixelBuffer(ResourceId id);
@@ -241,6 +246,18 @@ public:
     // Use setPixels or lockForWrite to allocate implicitly.
     void allocateForTesting(ResourceId id);
 
+    // Sets the current read fence. If a resource is locked for read
+    // and has read fences enabled, the resource will not allow writes
+    // until this fence has passed.
+    void setReadLockFence(Fence* fence) { m_currentReadLockFence = fence; }
+    Fence* getReadLockFence() { return m_currentReadLockFence; }
+
+    // Enable read lock fences for a specific resource.
+    void enableReadLockFences(ResourceProvider::ResourceId, bool enable);
+
+    // Indicates if we can currently lock this resource for write.
+    bool canLockForWrite(ResourceId);
+
 private:
     struct Resource {
         Resource();
@@ -263,6 +280,8 @@ private:
         bool markedForDeletion;
         bool pendingSetPixels;
         bool allocated;
+        bool enableReadLockFences;
+        scoped_refptr<Fence> readLockFence;
         gfx::Size size;
         GLenum format;
         // TODO(skyostil): Use a separate sampler object for filter state.
@@ -279,6 +298,9 @@ private:
     };
     typedef base::hash_map<int, Child> ChildMap;
 
+    bool readLockFenceHasPassed(Resource* resource) { return !resource->readLockFence ||
+                                                              resource->readLockFence->hasPassed(); }
+
     explicit ResourceProvider(OutputSurface*);
     bool initialize();
 
@@ -309,6 +331,8 @@ private:
 
     base::ThreadChecker m_threadChecker;
 
+    scoped_refptr<Fence> m_currentReadLockFence;
+
     DISALLOW_COPY_AND_ASSIGN(ResourceProvider);
 };