Fixes for nonmodal pinch zoom.

cc/layer_tree_host_impl.cc

 // 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.
 
 #include "cc/layer_tree_host_impl.h"
 
 #include <algorithm>
 
 #include "base/basictypes.h"
 #include "base/debug/trace_event.h"
@@ skipping 1223 matching lines @@
         m_rootScrollLayerImpl->scrollbarAnimationController()->didPinchGestureBegin();
 }
 
 void LayerTreeHostImpl::pinchGestureUpdate(float magnifyDelta, gfx::Point anchor)
 {
     TRACE_EVENT0("cc", "LayerTreeHostImpl::pinchGestureUpdate");
 
     if (!m_rootScrollLayerImpl)
         return;
 
-    if (m_previousPinchAnchor == gfx::Point())
-        m_previousPinchAnchor = anchor;
-
     // Keep the center-of-pinch anchor specified by (x, y) in a stable
     // position over the course of the magnify.
     float pageScaleDelta = m_pinchZoomViewport.pageScaleDelta();
-    gfx::PointF previousScaleAnchor = gfx::ScalePoint(m_previousPinchAnchor, 1 / pageScaleDelta);
+    gfx::PointF previousScaleAnchor = gfx::ScalePoint(anchor, 1 / pageScaleDelta);
     setPageScaleDelta(pageScaleDelta * magnifyDelta);
     pageScaleDelta = m_pinchZoomViewport.pageScaleDelta();
     gfx::PointF newScaleAnchor = gfx::ScalePoint(anchor, 1 / pageScaleDelta);
     gfx::Vector2dF move = previousScaleAnchor - newScaleAnchor;
 
     m_previousPinchAnchor = anchor;
 
     if (m_settings.pageScalePinchZoomEnabled) {
         // Compute the application of the delta with respect to the current page zoom of the page.
         move.Scale(1 / (m_pinchZoomViewport.pageScaleFactor() * m_deviceScaleFactor));
@@ skipping 248 matching lines @@
     ScrollbarAnimationController* scrollbarController = layer->scrollbarAnimationController();
     double monotonicTime = (time - base::TimeTicks()).InSecondsF();
     if (scrollbarController && scrollbarController->animate(monotonicTime))
         m_client->setNeedsRedrawOnImplThread();
 
     for (size_t i = 0; i < layer->children().size(); ++i)
         animateScrollbarsRecursive(layer->children()[i], time);
 }
 
 }  // namespace cc