Implement overlay scrollbar fade out for non-composited scrollers.

content/child/webthemeengine_impl_default.cc

 // Copyright 2014 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 "content/child/webthemeengine_impl_default.h"
 
 #include "build/build_config.h"
 #include "skia/ext/platform_canvas.h"
 #include "third_party/WebKit/public/platform/WebRect.h"
 #include "third_party/WebKit/public/platform/WebSize.h"
 #include "ui/native_theme/native_theme.h"
+#include "ui/native_theme/overlay_scrollbar_constants_aura.h"
 
 using blink::WebCanvas;
 using blink::WebColor;
 using blink::WebRect;
 using blink::WebThemeEngine;
 using blink::WebScrollbarOverlayColorTheme;
 
 namespace content {
 namespace {
 
@@ skipping 214 matching lines @@
     const blink::WebRect& rect,
     const WebThemeEngine::ExtraParams* extra_params) {
   ui::NativeTheme::ExtraParams native_theme_extra_params;
   GetNativeThemeExtraParams(
       part, state, extra_params, &native_theme_extra_params);
   ui::NativeTheme::GetInstanceForWeb()->Paint(
       canvas, NativeThemePart(part), NativeThemeState(state), gfx::Rect(rect),
       native_theme_extra_params);
 }
 
+void WebThemeEngineImpl::getOverlayScrollbarStyle(ScrollbarStyle* style) {
+  style->fadeOutDelaySeconds = ui::kOverlayScrollbarFadeOutDelay.InSecondsF();
+  style->fadeOutDurationSeconds =
+      ui::kOverlayScrollbarFadeOutDuration.InSecondsF();
+  // The other fields in this struct are used only on Android to draw solid
+  // color scrollbars. On other platforms the scrollbars are painted in
+  // NativeTheme so these fields are unused.
+}
+
 #if defined(OS_WIN)
 // static
 void WebThemeEngineImpl::cacheScrollBarMetrics(
     int32_t vertical_scroll_bar_width,
     int32_t horizontal_scroll_bar_height,
     int32_t vertical_arrow_bitmap_height,
     int32_t horizontal_arrow_bitmap_width) {
   g_vertical_scroll_bar_width = vertical_scroll_bar_width;
   g_horizontal_scroll_bar_height = horizontal_scroll_bar_height;
   g_vertical_arrow_bitmap_height = vertical_arrow_bitmap_height;
   g_horizontal_arrow_bitmap_width = horizontal_arrow_bitmap_width;
 }
 #endif
 
 }  // namespace content