First draft of TileManager's tile prioritzation system

cc/layer_tree_host_impl.h

 // Copyright 2011 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef CC_LAYER_TREE_HOST_IMPL_H_
 #define CC_LAYER_TREE_HOST_IMPL_H_
 
 #include "base/basictypes.h"
 #include "base/memory/scoped_ptr.h"
 #include "base/time.h"
@@ skipping 15 matching lines @@
 class FrameRateCounter;
 class HeadsUpDisplayLayerImpl;
 class LayerImpl;
 class LayerTreeHostImplTimeSourceAdapter;
 class PageScaleAnimation;
 class RenderPassDrawQuad;
 class ResourceProvider;
 struct RendererCapabilities;
 struct RenderingStats;
 
+enum WhichTree {
+  // Note: these must be 0 and 1 because we index with them in various places,
+  // e.g. in Tile::priority_.
+  ACTIVE_TREE = 0,
+  PENDING_TREE = 1
+};
+
 // LayerTreeHost->Proxy callback interface.
 class LayerTreeHostImplClient {
 public:
     virtual void didLoseContextOnImplThread() = 0;
     virtual void onSwapBuffersCompleteOnImplThread() = 0;
     virtual void onVSyncParametersChanged(base::TimeTicks timebase, base::TimeDelta interval) = 0;
     virtual void onCanDrawStateChanged(bool canDraw) = 0;
     virtual void setNeedsRedrawOnImplThread() = 0;
     virtual void setNeedsCommitOnImplThread() = 0;
     virtual void postAnimationEventsToMainThreadOnImplThread(scoped_ptr<AnimationEventsVector>, base::Time wallClockTime) = 0;
@@ skipping 307 matching lines @@
 
     size_t m_numImplThreadScrolls;
     size_t m_numMainThreadScrolls;
 
     DISALLOW_COPY_AND_ASSIGN(LayerTreeHostImpl);
 };
 
 }  // namespace cc
 
 #endif  // CC_LAYER_TREE_HOST_IMPL_H_