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 7f7df10798a7a2191f3b1c73daf947e8400a353c..957c1cea8f26752a2ca3c726364bffc191bb16a2 100644
--- a/cc/layer_tree_host_impl.cc
+++ b/cc/layer_tree_host_impl.cc
@@ -444,6 +444,11 @@ bool LayerTreeHostImpl::calculateRenderPasses(FrameData& frame)
     if (!canDraw() || !rootLayer())
       return false;
 
+    // Set the opacity of the pinch zoom scrollbars. This is done here
+    // so that it comes after the commit and we can directly set the
+    // opacity on the impl scrollbar layers.
+    activeTree()->SetPinchZoomScrollbarsVisibility();

[jamesr, 2013/02/26 20:48:46]

Why is this different for the pinch zoom scrollbars vs any other type of
scrollbar that has opacity animations?

[wjmaclean, 2013/03/01 15:30:32]

Because I had thought in the initial CL we would do this simply, and not via
animations. I've added animations now, so this will be gone in the next patch.

The existing animator for scrollbars requires that the scrollbars be managed by
a layerImpl, which is not the case for PZ scrollbars.

The new patch animates the scrollbars using vollick@'s animation framework,
which I think should replace the current ScrollbarAnimationController eventually
(soon, even).

+
     trackDamageForAllSurfaces(rootLayer(), *frame.renderSurfaceLayerList);
 
     TRACE_EVENT1("cc", "LayerTreeHostImpl::calculateRenderPasses", "renderSurfaceLayerList.size()", static_cast<long long unsigned>(frame.renderSurfaceLayerList->size()));
@@ -1353,6 +1358,7 @@ bool LayerTreeHostImpl::scrollBy(const gfx::Point& viewportPoint,
     }
 
     if (didScroll) {
+        activeTree()->UpdatePinchZoomScrollbarsIfNeeded();
         m_client->setNeedsCommitOnImplThread();
         m_client->setNeedsRedrawOnImplThread();
         m_client->renewTreePriority();
@@ -1371,6 +1377,8 @@ void LayerTreeHostImpl::scrollEnd()
     if (m_topControlsManager)
         m_topControlsManager->ScrollEnd();
     clearCurrentlyScrollingLayer();
+    if (activeTree()->HasPinchZoomScrollbars())
+        m_client->setNeedsRedrawOnImplThread();
 }
 
 void LayerTreeHostImpl::pinchGestureBegin()