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

cc/layer_tree_host.cc

Index: cc/layer_tree_host.cc
diff --git a/cc/layer_tree_host.cc b/cc/layer_tree_host.cc
index 862cccd5f084b45ee9bd25b4bb9da964a53a68ce..fadee527be9dbfaf746f23f779b5e39e5472e7ba 100644
--- a/cc/layer_tree_host.cc
+++ b/cc/layer_tree_host.cc
@@ -276,7 +276,7 @@ static void pushPropertiesRecursive(Layer* layer, LayerImpl* layerImpl)
 
     const std::vector<scoped_refptr<Layer> >& children = layer->children();
     const ScopedPtrVector<LayerImpl>& implChildren = layerImpl->children();
-    DCHECK_EQ(children.size(), implChildren.size());
+    DCHECK(children.size() <= implChildren.size());

[Ian Vollick, 2013/01/15 20:33:48]

I think we need to be more explicit about impl-only layers here. We should be
able to DCHECK that the number of children exactly equals (implChildren.size() -
num-impl-only-layers).

 
     for (size_t i = 0; i < children.size(); ++i) {
         pushPropertiesRecursive(children[i].get(), implChildren[i]);
@@ -330,6 +330,9 @@ void LayerTreeHost::finishCommitOnImplThread(LayerTreeHostImpl* hostImpl)
     syncTree->set_background_color(m_backgroundColor);
     syncTree->set_has_transparent_background(m_hasTransparentBackground);
 
+    if (m_settings.pageScalePinchZoomEnabled)
+        hostImpl->pinchZoomViewport().AddPinchZoomScrollbarsToTree(syncTree);

[Ian Vollick, 2013/01/15 20:33:48]

I don't like that this function is getting littered with code to add special
layers. I think that if we were to make impl-only layers a more official thing,
we could replace both the hud and ping zoom scrollbar stuff here with a call to
addImplOnlyLayers(dataRequiredByThisFunction).

+
     hostImpl->setViewportSize(layoutViewportSize(), deviceViewportSize());
     hostImpl->setDeviceScaleFactor(deviceScaleFactor());
     hostImpl->setPageScaleFactorAndLimits(m_pageScaleFactor, m_minPageScaleFactor, m_maxPageScaleFactor);