Make new-style page scale work on Android.

cc/layer_tree_impl.cc

Index: cc/layer_tree_impl.cc
diff --git a/cc/layer_tree_impl.cc b/cc/layer_tree_impl.cc
index 769639a4091c9dc2e987c7c7b546658329f23489..4650f277d13f7be0d5f7accea0d6662724e01f14 100644
--- a/cc/layer_tree_impl.cc
+++ b/cc/layer_tree_impl.cc
@@ -85,28 +85,21 @@ void LayerTreeImpl::UpdateMaxScrollOffset() {
   if (!root_scroll_layer() || !root_scroll_layer()->children().size())
     return;
 
-  gfx::SizeF view_bounds = device_viewport_size();
-  if (LayerImpl* clip_layer = root_scroll_layer()->parent()) {
-    // Compensate for non-overlay scrollbars.
-    if (clip_layer->masksToBounds())
-      view_bounds = gfx::ScaleSize(clip_layer->bounds(), device_scale_factor());
-  }
-
-  gfx::Size content_bounds = ContentSize();
-  if (settings().pageScalePinchZoomEnabled) {
-    // Pinch with pageScale scrolls entirely in layout space.  ContentSize
-    // returns the bounds including the page scale factor, so calculate the
-    // pre page-scale layout size here.
-    float page_scale_factor = pinch_zoom_viewport().page_scale_factor();
-    content_bounds.set_width(content_bounds.width() / page_scale_factor);
-    content_bounds.set_height(content_bounds.height() / page_scale_factor);
-  } else {
+  gfx::SizeF view_bounds;
+  if (!settings().pageScalePinchZoomEnabled) {
+    view_bounds = device_viewport_size();
+    if (LayerImpl* clip_layer = root_scroll_layer()->parent()) {
+      // Compensate for non-overlay scrollbars.
+      if (clip_layer->masksToBounds())
+        view_bounds = gfx::ScaleSize(clip_layer->bounds(), device_scale_factor());

[danakj, 2013/01/17 18:02:49]

This bound here (and above) is in physical pixels, but the else{} clause is in
logical pixels? It seems like this code could be using the layout viewport size
and not scaling the clip layer's bounds?

[aelias_OOO_until_Jul13, 2013/01/17 19:59:46]

This clause is for the old coordinate space so it uses totally different
assumptions about the semantics.  I'm just leaving it unchanged to avoid
breaking Android before the transition is complete.

+    }
     view_bounds.Scale(1 / pinch_zoom_viewport().page_scale_delta());
+  } else {
+    view_bounds = layout_viewport_size();
   }
 
-  gfx::Vector2dF max_scroll = gfx::Rect(content_bounds).bottom_right() -
+  gfx::Vector2dF max_scroll = gfx::Rect(ScrollableSize()).bottom_right() -

[danakj, 2013/01/17 18:02:49]

I do like this :)

       gfx::RectF(view_bounds).bottom_right();
-  max_scroll.Scale(1 / device_scale_factor());
 
   // The viewport may be larger than the contents in some cases, such as
   // having a vertical scrollbar but no horizontal overflow.
@@ -175,12 +168,10 @@ const LayerTreeImpl::LayerList& LayerTreeImpl::RenderSurfaceLayerList() const {
   return render_surface_layer_list_;
 }
 
-gfx::Size LayerTreeImpl::ContentSize() const {
-  // TODO(aelias): Hardcoding the first child here is weird. Think of
-  // a cleaner way to get the contentBounds on the Impl side.
+gfx::Size LayerTreeImpl::ScrollableSize() const {
   if (!root_scroll_layer() || root_scroll_layer()->children().empty())
     return gfx::Size();
-  return root_scroll_layer()->children()[0]->contentBounds();
+  return root_scroll_layer()->children()[0]->bounds();
 }
 
 LayerImpl* LayerTreeImpl::LayerById(int id) {