Ensure that the focus ring in the bookmarks bar does not paint outside the parent view.

ui/views/controls/scroll_view.cc

 // Copyright (c) 2012 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 "ui/views/controls/scroll_view.h"
 
 #include "base/feature_list.h"
 #include "base/logging.h"
 #include "base/macros.h"
 #include "ui/base/material_design/material_design_controller.h"
@@ skipping 14 matching lines @@
 
 const base::Feature kToolkitViewsScrollWithLayers {
   "ToolkitViewsScrollWithLayers",
 #if defined(OS_MACOSX)
       base::FEATURE_ENABLED_BY_DEFAULT
 #else
       base::FEATURE_DISABLED_BY_DEFAULT
 #endif
 };
 
+// Set if the kToolkitViewsScrollWithLayers feature is enabled.
+// TODO(ananta)
+// Remove this when the feature is enabled by default.
+bool g_scroll_with_layers_enabled = false;
+
 class ScrollCornerView : public View {
  public:
   ScrollCornerView() {}
 
   void OnPaint(gfx::Canvas* canvas) override {
     ui::NativeTheme::ExtraParams ignored;
     GetNativeTheme()->Paint(canvas->sk_canvas(),
                             ui::NativeTheme::kScrollbarCorner,
                             ui::NativeTheme::kNormal,
                             GetLocalBounds(),
@@ skipping 15 matching lines @@
   return current_pos;
 }
 
 // Make sure the content is not scrolled out of bounds
 void ConstrainScrollToBounds(View* viewport, View* view) {
   if (!view)
     return;
 
   // Note that even when ScrollView::ScrollsWithLayers() is true, the header row
   // scrolls by repainting.
-  const bool scrolls_with_layers = viewport->layer() != nullptr;
+  const bool scrolls_with_layers =
+      g_scroll_with_layers_enabled && viewport->layer() != nullptr;

[sky, 2017/04/17 15:24:01]

Make ScrollView have a member for scroll_with_layers_enabled is true and then
pass it into this function. In other words, no global for
g_scroll_with_layers_enabled.

[ananta, 2017/04/18 03:04:25]

Done.

   if (scrolls_with_layers) {
     DCHECK(view->layer());
     DCHECK_EQ(0, view->x());
     DCHECK_EQ(0, view->y());
   }
   gfx::ScrollOffset offset = scrolls_with_layers
                                  ? view->layer()->CurrentScrollOffset()
                                  : gfx::ScrollOffset(-view->x(), -view->y());
 
   int x = CheckScrollBounds(viewport->width(), view->width(), offset.x());
@@ skipping 78 matching lines @@
   AddChildView(header_viewport_);
 
   // Don't add the scrollbars as children until we discover we need them
   // (ShowOrHideScrollBar).
   horiz_sb_->SetVisible(false);
   horiz_sb_->set_controller(this);
   vert_sb_->SetVisible(false);
   vert_sb_->set_controller(this);
   corner_view_->SetVisible(false);
 
-  if (!base::FeatureList::IsEnabled(kToolkitViewsScrollWithLayers))
+  g_scroll_with_layers_enabled =
+      base::FeatureList::IsEnabled(kToolkitViewsScrollWithLayers);
+  if (!g_scroll_with_layers_enabled)
     return;
+
   EnableViewPortLayer();
 }
 
 ScrollView::~ScrollView() {
   // The scrollbars may not have been added, delete them to ensure they get
   // deleted.
   delete horiz_sb_;
   delete vert_sb_;
   delete corner_view_;
 }
@@ skipping 339 matching lines @@
 }
 
 const char* ScrollView::GetClassName() const {
   return kViewClassName;
 }
 
 void ScrollView::OnNativeThemeChanged(const ui::NativeTheme* theme) {
   UpdateBorder();
 }
 
+void ScrollView::OnChildLayerChanged(View* child) {
+  EnableViewPortLayer();
+}
+
 void ScrollView::ScrollToPosition(ScrollBar* source, int position) {
   if (!contents_)
     return;
 
   gfx::ScrollOffset offset = CurrentOffset();
   if (source == horiz_sb_ && horiz_sb_->visible()) {
     position = AdjustPosition(offset.x(), position, contents_->width(),
                               contents_viewport_->width());
     if (offset.x() == position)
       return;
@@ skipping 170 matching lines @@
     // and commits a frame, which isn't true in some tests.
     // See http://crbug.com/637521.
     OnLayerScrolled(offset);
   } else {
     contents_->SetPosition(gfx::Point(-offset.x(), -offset.y()));
     ScrollHeader();
   }
 }
 
 bool ScrollView::ScrollsWithLayers() const {
+  if (!g_scroll_with_layers_enabled)
+    return false;
   // Just check for the presence of a layer since it's cheaper than querying the
   // Feature flag each time.
   return contents_viewport_->layer() != nullptr;
 }
 
 void ScrollView::EnableViewPortLayer() {
+  if (viewport_layer_enabled_)
+    return;
+
+  viewport_layer_enabled_ = true;
   background_color_ = SK_ColorWHITE;
   contents_viewport_->set_background(
       Background::CreateSolidBackground(background_color_));
   contents_viewport_->SetPaintToLayer();
   contents_viewport_->layer()->SetMasksToBounds(true);
 }
 
 void ScrollView::OnLayerScrolled(const gfx::ScrollOffset&) {
   UpdateScrollBarPositions();
   ScrollHeader();
@@ skipping 94 matching lines @@
 
 VariableRowHeightScrollHelper::RowInfo
     FixedRowHeightScrollHelper::GetRowInfo(int y) {
   if (y < top_margin_)
     return RowInfo(0, top_margin_);
   return RowInfo((y - top_margin_) / row_height_ * row_height_ + top_margin_,
                  row_height_);
 }
 
 }  // namespace views