Fix scrollbar buttons on ChromeOS.

ui/native_theme/native_theme_base.cc

Index: ui/native_theme/native_theme_base.cc
diff --git a/ui/native_theme/native_theme_base.cc b/ui/native_theme/native_theme_base.cc
index 548b4a5cf695869c665d8eee425948b31e0d60af..482037ea6513e271671bcfabf6129b18fc4c653d 100644
--- a/ui/native_theme/native_theme_base.cc
+++ b/ui/native_theme/native_theme_base.cc
@@ -115,10 +115,14 @@ gfx::Size NativeThemeBase::GetPartSize(Part part,
       return gfx::Size(kCheckboxAndRadioWidth, kCheckboxAndRadioHeight);
     case kScrollbarDownArrow:
     case kScrollbarUpArrow:
-      return gfx::Size(scrollbar_width_, scrollbar_button_length_);
+      if (HasScrollbarButtons())
+        return gfx::Size(scrollbar_width_, kDefaultScrollbarButtonLength);
+      return gfx::Size(0, 0);
     case kScrollbarLeftArrow:
     case kScrollbarRightArrow:
-      return gfx::Size(scrollbar_button_length_, scrollbar_width_);
+      if (HasScrollbarButtons())
+        return gfx::Size(kDefaultScrollbarButtonLength, scrollbar_width_);
+      return gfx::Size(0, 0);
     case kScrollbarHorizontalThumb:
       // This matches Firefox on Linux.
       return gfx::Size(2 * scrollbar_width_, scrollbar_width_);
@@ -221,7 +225,7 @@ void NativeThemeBase::Paint(SkCanvas* canvas,
     case kScrollbarUpArrow:
     case kScrollbarLeftArrow:
     case kScrollbarRightArrow:
-      if (scrollbar_button_length_ > 0)
+      if (HasScrollbarButtons())
         PaintArrowButton(canvas, rect, part, state);
       break;
     case kScrollbarHorizontalThumb:
@@ -265,10 +269,7 @@ void NativeThemeBase::Paint(SkCanvas* canvas,
   canvas->restore();
 }
 
-NativeThemeBase::NativeThemeBase()
-    : scrollbar_width_(kDefaultScrollbarWidth),
-      scrollbar_button_length_(kDefaultScrollbarButtonLength) {
-}
+NativeThemeBase::NativeThemeBase() : scrollbar_width_(kDefaultScrollbarWidth) {}
 
 NativeThemeBase::~NativeThemeBase() {
 }