Fixed rounding issue on scrollbar rasterization.

cc/test/fake_scrollbar.cc

 // Copyright 2013 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 "cc/test/fake_scrollbar.h"
 
 #include "third_party/skia/include/core/SkCanvas.h"
+#include "ui/gfx/skia_util.h"
 
 namespace cc {
 
 FakeScrollbar::FakeScrollbar()
     : paint_(false),
       has_thumb_(false),
       is_overlay_(false),
       thumb_thickness_(10),
       thumb_length_(5),
       track_rect_(0, 0, 100, 10),
@@ skipping 37 matching lines @@
 }
 
 void FakeScrollbar::PaintPart(SkCanvas* canvas,
                              ScrollbarPart part,
                              const gfx::Rect& content_rect) {
   if (!paint_)
     return;
 
   // Fill the scrollbar with a different color each time.
   fill_color_++;
-  canvas->clear(SK_ColorBLACK | fill_color_);
+  SkPaint paint;
+  paint.setAntiAlias(false);
+  paint.setColor(paint_fill_color());
+  paint.setStyle(SkPaint::kFill_Style);
+
+  // Emulate the how the real scrollbar works by using scrollbar's rect for
+  // TRACK and the given content_rect for the THUMB
+  SkRect rect = part == TRACK ? RectToSkRect(TrackRect())
+                              : RectToSkRect(content_rect);
+  canvas->drawRect(rect, paint);
 }
 
 }  // namespace cc