Aura overlay scrollbars adjust color for dark backgrounds

content/child/webthemeengine_impl_default.h

Index: content/child/webthemeengine_impl_default.h
diff --git a/content/child/webthemeengine_impl_default.h b/content/child/webthemeengine_impl_default.h
index 36ddb6bf7f569f0b8b67eeea0580f7b9b12d0834..9d413729007f0dd3daba3d8247ac03f7ca955435 100644
--- a/content/child/webthemeengine_impl_default.h
+++ b/content/child/webthemeengine_impl_default.h
@@ -9,6 +9,7 @@
 
 #include "build/build_config.h"
 #include "third_party/WebKit/public/platform/WebThemeEngine.h"
+#include "ui/native_theme/native_theme.h"
 
 namespace content {
 
@@ -21,12 +22,14 @@ class WebThemeEngineImpl : public blink::WebThemeEngine {
              blink::WebThemeEngine::State state,
              const blink::WebRect& rect,
              const blink::WebThemeEngine::ExtraParams* extra_params) override;
-  virtual void paintStateTransition(blink::WebCanvas* canvas,
-                                    blink::WebThemeEngine::Part part,
-                                    blink::WebThemeEngine::State startState,
-                                    blink::WebThemeEngine::State endState,
-                                    double progress,
-                                    const blink::WebRect& rect);
+  virtual void paintStateTransition(
+      blink::WebCanvas* canvas,
+      blink::WebThemeEngine::Part part,
+      blink::WebThemeEngine::State startState,
+      blink::WebThemeEngine::State endState,
+      double progress,
+      const blink::WebRect& rect,
+      ui::NativeTheme::ScrollbarOverlayColorTheme theme);

[bokan, 2016/10/21 16:57:14]

This should take a blink::WebThemeEngine::ScrollbarOverlayColorTheme, and then
add a NativeThemeScrollbarOverlayColorTheme() function to convert between to the
ui::NativeTheme enum. Like how it works for the above params.

 #if defined(OS_WIN)
   // Caches the scrollbar metrics. These are retrieved in the browser and passed
   // to the renderer in RendererPreferences because the required Windows system