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

cc/pinch_zoom_viewport.cc

Index: cc/pinch_zoom_viewport.cc
diff --git a/cc/pinch_zoom_viewport.cc b/cc/pinch_zoom_viewport.cc
index dab6c9ca823cc57b18ef53eb3c503f41a5948813..1fd24343f0c32a4fa31ac567bda8d6d62e28d669 100644
--- a/cc/pinch_zoom_viewport.cc
+++ b/cc/pinch_zoom_viewport.cc
@@ -5,18 +5,26 @@
 #include "cc/pinch_zoom_viewport.h"
 
 #include "base/logging.h"
+#include "cc/layer_tree_host_impl.h"
+#include "cc/layer_tree_impl.h"
 
 namespace cc {
 
-PinchZoomViewport::PinchZoomViewport()
+PinchZoomViewport::PinchZoomViewport(LayerTreeHostImpl* owner)
     : page_scale_factor_(1),
       page_scale_delta_(1),
       sent_page_scale_delta_(1),
       min_page_scale_factor_(0),
       max_page_scale_factor_(0),
-      device_scale_factor_(1) {
+      device_scale_factor_(1),
+      vertical_scrollbar_client_(WebKit::WebScrollbar::Vertical, this),
+      horizontal_scrollbar_client_(WebKit::WebScrollbar::Horizontal, this),
+      owner_(owner) {
+  DCHECK(owner_);
 }
 
+PinchZoomViewport::~PinchZoomViewport() {}
+
 void PinchZoomViewport::set_page_scale_delta(float delta) {
   // Clamp to the current min/max limits.
   float totalPageScaleFactor = page_scale_factor_ * delta;
@@ -107,4 +115,47 @@ gfx::Transform PinchZoomViewport::ImplTransform(
   return transform;
 }
 
+// Implement here to avoid having to include LayerTreeHostImpl.h
+// in PinchZoomViewport.h.
+LayerImpl* PinchZoomViewport::root_scroll_layer() {
+  return owner_->rootScrollLayer();
+}
+
+LayerImpl* PinchZoomViewport::currently_scrolling_layer() const {
+  return owner_->currentlyScrollingLayer();
+}
+
+void PinchZoomViewport::AddPinchZoomScrollbarsToTree(LayerTreeImpl* tree_impl) {
+  DCHECK(tree_impl);
+  LayerImpl* root = tree_impl->RootLayer();
+
+  // TODO(wjmaclean) - I was told that TreeSynchronizer would kill any impl-side layer
+  // that does not have a matching main-thread layer, but this seems not to be the case
+  // as the pinch-zoom scrollbar layers seem to be surviving the sync.
+  // Note: the survival of the pinch-zoom scrollbars can be leveraged, by only re-creating
+  // them when (if ever) they get clobbered. Although PinchZoomScrollbarLayerImpl is
+  // meant to be a lighweight wrapper, it is still derived from LayerImpl and thus has
+  // some overhead.
+  for (int id = -1; id >= -2; --id)
+    if (LayerImpl* layer = tree_impl->LayerById(id))
+      root->removeChild(layer);
+
+  // WJM - set bounds & geomtery & drawsContent ...
+  scoped_ptr<PinchZoomScrollbarLayerImpl> vertical_scrollbar =
+    PinchZoomScrollbarLayerImpl::create(
+        tree_impl, -1, &vertical_scrollbar_client_);
+  vertical_scrollbar->setDrawsContent(true);
+  vertical_scrollbar_client_.RefreshSizeAndPosition(vertical_scrollbar.get());
+
+  root->addChild(vertical_scrollbar.PassAs<LayerImpl>());
+
+  scoped_ptr<PinchZoomScrollbarLayerImpl> horizontal_scrollbar =
+    PinchZoomScrollbarLayerImpl::create(
+        tree_impl, -2, &horizontal_scrollbar_client_);
+  horizontal_scrollbar->setDrawsContent(true);
+  horizontal_scrollbar_client_.RefreshSizeAndPosition(horizontal_scrollbar.get());
+
+  root->addChild(horizontal_scrollbar.PassAs<LayerImpl>());
+}
+
 }  // namespace cc