Fix scrollbar buttons on ChromeOS.

ui/native_theme/native_theme_base.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/native_theme/native_theme_base.h"
 
 #include <limits>
 #include <memory>
 
 #include "base/command_line.h"
@@ skipping 97 matching lines @@
     case kMenuPopupBackground:
       return gfx::Size();  // No default size.
     case kMenuItemBackground:
     case kProgressBar:
     case kPushButton:
       return gfx::Size();  // No default size.
     case kRadio:
       return gfx::Size(kCheckboxAndRadioWidth, kCheckboxAndRadioHeight);
     case kScrollbarDownArrow:
     case kScrollbarUpArrow:
-      return gfx::Size(scrollbar_width_, scrollbar_button_length_);
     case kScrollbarLeftArrow:
     case kScrollbarRightArrow:
-      return gfx::Size(scrollbar_button_length_, scrollbar_width_);

[Evan Stade, 2016/05/23 22:30:59]

why not leave most stuff alone, but change scrollbar_width_ to 0 if length is 0?

[Bret, 2016/05/23 22:53:15]

That wasn't actually the problem. I thought this was unused which is why I
removed it, but you're right it looks like native_scroll_bar_views.cc is using
it. I'll change this back.

[Bret, 2016/05/23 23:44:06]

Done.

+      return gfx::Size();  // No default size.
     case kScrollbarHorizontalThumb:
       // This matches Firefox on Linux.
       return gfx::Size(2 * scrollbar_width_, scrollbar_width_);
     case kScrollbarVerticalThumb:
       // This matches Firefox on Linux.
       return gfx::Size(scrollbar_width_, 2 * scrollbar_width_);
     case kScrollbarHorizontalTrack:
       return gfx::Size(0, scrollbar_width_);
     case kScrollbarVerticalTrack:
       return gfx::Size(scrollbar_width_, 0);
@@ skipping 82 matching lines @@
     case kPushButton:
       PaintButton(canvas, state, rect, extra.button);
       break;
     case kRadio:
       PaintRadio(canvas, state, rect, extra.button);
       break;
     case kScrollbarDownArrow:
     case kScrollbarUpArrow:
     case kScrollbarLeftArrow:
     case kScrollbarRightArrow:
-      if (scrollbar_button_length_ > 0)
+      if (HasScrollbarButtons())

[esprehn, 2016/05/23 23:11:19]

how did we get here if it was zero size?

[Bret, 2016/05/23 23:44:06]

It looks like ScrollbarThemeAura just calls paint for every piece of the
scrollbar without checking their sizes.

         PaintArrowButton(canvas, rect, part, state);
       break;
     case kScrollbarHorizontalThumb:
     case kScrollbarVerticalThumb:
       PaintScrollbarThumb(canvas, part, state, rect);
       break;
     case kScrollbarHorizontalTrack:
     case kScrollbarVerticalTrack:
       PaintScrollbarTrack(canvas, part, state, extra.scrollbar_track, rect);
       break;
@@ skipping 23 matching lines @@
       NOTIMPLEMENTED();
       break;
     default:
       NOTREACHED() << "Unknown theme part: " << part;
       break;
   }
 
   canvas->restore();
 }
 
-NativeThemeBase::NativeThemeBase()
-    : scrollbar_width_(kDefaultScrollbarWidth),
-      scrollbar_button_length_(kDefaultScrollbarButtonLength) {
-}
+NativeThemeBase::NativeThemeBase() : scrollbar_width_(kDefaultScrollbarWidth) {}
 
 NativeThemeBase::~NativeThemeBase() {
 }
 
 void NativeThemeBase::PaintArrowButton(
     SkCanvas* canvas,
     const gfx::Rect& rect, Part direction, State state) const {
   SkPaint paint;
 
   // Calculate button color.
@@ skipping 726 matching lines @@
   SkScalar min_diff = Clamp((hsv1[1] + hsv2[1]) * 1.2f, 0.28f, 0.5f);
   SkScalar diff = Clamp(fabs(hsv1[2] - hsv2[2]) / 2, min_diff, 0.5f);
 
   if (hsv1[2] + hsv2[2] > 1.0)
     diff = -diff;
 
   return SaturateAndBrighten(hsv2, -0.2f, diff);
 }
 
 }  // namespace ui