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 e22698635ed14a60b99a8d2eaeb5c276b6f260a1..ec272ce0a734a395a1992453ead2c51ac1a9aad8 100644
--- a/cc/layer_tree_host.cc
+++ b/cc/layer_tree_host.cc
@@ -23,7 +23,11 @@
 #include "cc/math_util.h"
 #include "cc/occlusion_tracker.h"
 #include "cc/overdraw_metrics.h"
+#include "cc/pinch_zoom_scrollbar.h"
+#include "cc/pinch_zoom_scrollbar_geometry.h"
+#include "cc/pinch_zoom_scrollbar_painter.h"
 #include "cc/prioritized_resource_manager.h"
+#include "cc/scrollbar_layer.h"
 #include "cc/single_thread_proxy.h"
 #include "cc/switches.h"
 #include "cc/thread.h"
@@ -328,6 +332,14 @@ void LayerTreeHost::FinishCommitOnImplThread(LayerTreeHostImpl* host_impl) {
       sync_tree->ResetContentsTexturesPurged();
   }
 
+  sync_tree->SetPinchZoomHorizontalLayerId(
+      pinch_zoom_scrollbar_horizontal_ ?
+          pinch_zoom_scrollbar_horizontal_->id() : Layer::INVALID_ID);
+
+  sync_tree->SetPinchZoomVerticalLayerId(
+      pinch_zoom_scrollbar_vertical_ ?
+          pinch_zoom_scrollbar_vertical_->id() : Layer::INVALID_ID);
+
   if (!settings_.implSidePainting) {
     // If we're not in impl-side painting, the tree is immediately
     // considered active.
@@ -340,8 +352,70 @@ void LayerTreeHost::FinishCommitOnImplThread(LayerTreeHostImpl* host_impl) {
   commit_number_++;
 }
 
+void LayerTreeHost::SetPinchZoomScrollbarsBoundsAndPosition()
+{
+    if (!pinch_zoom_scrollbar_horizontal_ || !pinch_zoom_scrollbar_vertical_)
+        return;
+
+    gfx::Size size = layout_viewport_size();
+    int track_width = PinchZoomScrollbarGeometry::kTrackWidth;
+
+    pinch_zoom_scrollbar_horizontal_->SetBounds(
+        gfx::Size(size.width() - track_width, track_width));
+    pinch_zoom_scrollbar_horizontal_->SetPosition(
+        gfx::PointF(0, size.height() - track_width));
+
+    pinch_zoom_scrollbar_vertical_->SetBounds(
+        gfx::Size(track_width, size.height() - track_width));
+    pinch_zoom_scrollbar_vertical_->SetPosition(
+        gfx::PointF(size.width() - track_width, 0));
+}
+
+static scoped_refptr<ScrollbarLayer> CreatePinchZoomScrollbar(
+    WebKit::WebScrollbar::Orientation orientation, LayerTreeHost* owner)
+{
+  scoped_refptr<ScrollbarLayer> scrollbar_layer = ScrollbarLayer::Create(
+      make_scoped_ptr(
+          new PinchZoomScrollbar(orientation, owner))
+            .PassAs<WebKit::WebScrollbar>(),
+      scoped_ptr<ScrollbarThemePainter>(new PinchZoomScrollbarPainter).Pass(),
+      scoped_ptr<WebKit::WebScrollbarThemeGeometry>(
+          new PinchZoomScrollbarGeometry).Pass(),
+      Layer::PINCH_ZOOM_ROOT_SCROLL_LAYER_ID);
+  scrollbar_layer->SetIsDrawable(true);
+  scrollbar_layer->SetOpacity(0.f);
+  return scrollbar_layer;
+}
+
+void LayerTreeHost::CreateAndAddPinchZoomScrollbars()
+{
+  bool needs_properties_updated = false;
+
+  if (!pinch_zoom_scrollbar_horizontal_ || !pinch_zoom_scrollbar_vertical_) {
+    pinch_zoom_scrollbar_horizontal_ =
+        CreatePinchZoomScrollbar(WebKit::WebScrollbar::Horizontal, this);
+    pinch_zoom_scrollbar_vertical_ =
+        CreatePinchZoomScrollbar( WebKit::WebScrollbar::Vertical, this);
+    needs_properties_updated = true;
+  }
+
+  DCHECK(pinch_zoom_scrollbar_horizontal_ && pinch_zoom_scrollbar_vertical_);
+
+  if (!pinch_zoom_scrollbar_horizontal_->parent())
+      root_layer_->AddChild(pinch_zoom_scrollbar_horizontal_);
+
+  if (!pinch_zoom_scrollbar_vertical_->parent())
+      root_layer_->AddChild(pinch_zoom_scrollbar_vertical_);
+
+  if (needs_properties_updated)
+      SetPinchZoomScrollbarsBoundsAndPosition();
+}
+
 void LayerTreeHost::WillCommit() {
   client_->willCommit();
+
+  if (settings().usePinchZoomScrollbars)
+    CreateAndAddPinchZoomScrollbars();
 }
 
 void LayerTreeHost::UpdateHudLayer() {
@@ -470,6 +544,12 @@ void LayerTreeHost::SetRootLayer(scoped_refptr<Layer> root_layer) {
   if (hud_layer_)
     hud_layer_->RemoveFromParent();
 
+  if (pinch_zoom_scrollbar_horizontal_)
+    pinch_zoom_scrollbar_horizontal_->RemoveFromParent();
+
+  if (pinch_zoom_scrollbar_vertical_)
+    pinch_zoom_scrollbar_vertical_->RemoveFromParent();
+
   SetNeedsFullTreeSync();
 }
 
@@ -493,6 +573,7 @@ void LayerTreeHost::SetViewportSize(gfx::Size layout_viewport_size,
   layout_viewport_size_ = layout_viewport_size;
   device_viewport_size_ = device_viewport_size;
 
+  SetPinchZoomScrollbarsBoundsAndPosition();
   SetNeedsCommit();
 }
 
@@ -584,6 +665,10 @@ static Layer* FindFirstScrollableLayer(Layer* layer) {
   return NULL;
 }
 
+const Layer* LayerTreeHost::RootScrollLayer() const {
+  return FindFirstScrollableLayer(root_layer_.get());
+}
+
 void LayerTreeHost::UpdateLayers(Layer* root_layer,
                                  ResourceUpdateQueue* queue) {
   TRACE_EVENT0("cc", "LayerTreeHost::UpdateLayers");