Implement pinch-zoom scaling for main-frame scrollbars and pinch-zoom overlay scrollbars.

cc/layer_tree_host_impl.cc

Index: cc/layer_tree_host_impl.cc
diff --git a/cc/layer_tree_host_impl.cc b/cc/layer_tree_host_impl.cc
index 38ef549549cb875845e5b304018822d852616edf..0cfdfcc378da6cf1c03e62eca660efa978d7b076 100644
--- a/cc/layer_tree_host_impl.cc
+++ b/cc/layer_tree_host_impl.cc
@@ -1196,6 +1196,8 @@ InputHandlerClient::ScrollStatus LayerTreeHostImpl::scrollBegin(gfx::Point viewp
         if (layerImpl->tryScroll(deviceViewportPoint, type) == ScrollOnMainThread) {
             m_numMainThreadScrolls++;
             UMA_HISTOGRAM_BOOLEAN("TryScroll.SlowScroll", true);
+            if (activeTree()->HasPinchZoomScrollbars())

[enne (OOO), 2013/03/06 19:32:58]

Can LayerTreeHostImpl be less aware of pinch zoom scrollbars and instead just
have an API on LayerTreeImpl like DidBeginScroll(), DidUpdateScroll(),
DidEndScroll()? This would encapsulate the pinch zoom scrollbar updates and
animations inside of LayerTreeImpl and LayerTreeImpl would no longer need to
expose so many accessors and updaters.

[wjmaclean, 2013/03/06 22:36:53]

Sounds like a good idea! Done.

+                activeTree()->FadeInPinchZoomScrollbars();
             return ScrollOnMainThread;
         }
 
@@ -1209,6 +1211,8 @@ InputHandlerClient::ScrollStatus LayerTreeHostImpl::scrollBegin(gfx::Point viewp
         if (status == ScrollOnMainThread) {
             m_numMainThreadScrolls++;
             UMA_HISTOGRAM_BOOLEAN("TryScroll.SlowScroll", true);
+            if (activeTree()->HasPinchZoomScrollbars())
+                activeTree()->FadeInPinchZoomScrollbars();
             return ScrollOnMainThread;
         }
 
@@ -1231,6 +1235,8 @@ InputHandlerClient::ScrollStatus LayerTreeHostImpl::scrollBegin(gfx::Point viewp
         m_numImplThreadScrolls++;
         m_client->renewTreePriority();
         UMA_HISTOGRAM_BOOLEAN("TryScroll.SlowScroll", false);
+        if (activeTree()->HasPinchZoomScrollbars())
+            activeTree()->FadeInPinchZoomScrollbars();
         return ScrollStarted;
     }
     return ScrollIgnored;
@@ -1354,6 +1360,8 @@ bool LayerTreeHostImpl::scrollBy(const gfx::Point& viewportPoint,
             break;
     }
 
+    activeTree()->UpdatePinchZoomScrollbarsIfNeeded(
+      LayerTreeImpl::UPDATE_IMPL_THREAD_SCROLL);
     if (didScroll) {
         m_client->setNeedsCommitOnImplThread();
         m_client->setNeedsRedrawOnImplThread();
@@ -1373,6 +1381,8 @@ void LayerTreeHostImpl::scrollEnd()
     if (m_topControlsManager)
         m_topControlsManager->ScrollEnd();
     clearCurrentlyScrollingLayer();
+    if (activeTree()->HasPinchZoomScrollbars())
+        activeTree()->FadeOutPinchZoomScrollbars();
 }
 
 void LayerTreeHostImpl::pinchGestureBegin()