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_);
+
+  if (part == TRACK) {
+    SkPaint paint;
+    paint.setAntiAlias(false);
+    paint.setColor(get_color());
+    paint.setStyle(SkPaint::kFill_Style);
+    canvas->drawRect(RectToSkRect(TrackRect()), paint);

[danakj, 2014/02/18 20:43:30]

Hm.. why isn't this able to just paint the |content_rect| then? Should we be
doing this for all parts not just TRACK?

[bokan, 2014/02/18 21:48:15]

The real ScrollbarImpl's PaintPart method only uses content_rect to draw the
thumb. Everything else (there's really only TRACK and THUMB) uses the
scrollbar's TrackRect() so this represents the real scrollbar painting code more
accurately. (In fact, using content_rect here makes the test pass even if the
bug is still in the code)

I've changed the clear method below to fillRect the content_rect to be
consistent with the real PaintPart for the thumb. 

+  } else {
+    canvas->clear(get_color());
+  }
 }
 
 }  // namespace cc