Fixed rounding issue on scrollbar rasterization.

cc/test/fake_scrollbar.cc

Index: cc/test/fake_scrollbar.cc
diff --git a/cc/test/fake_scrollbar.cc b/cc/test/fake_scrollbar.cc
index 7285660f17016fc5be6e56070a40a817d7dfe0e2..f500a2a2861e99b17f2c832f1f89db7cd7af2a41 100644
--- a/cc/test/fake_scrollbar.cc
+++ b/cc/test/fake_scrollbar.cc
@@ -5,6 +5,7 @@
 #include "cc/test/fake_scrollbar.h"
 
 #include "third_party/skia/include/core/SkCanvas.h"
+#include "ui/gfx/skia_util.h"
 
 namespace cc {
 
@@ -62,7 +63,16 @@ void FakeScrollbar::PaintPart(SkCanvas* canvas,
 
   // 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