Fixed rounding issue on scrollbar rasterization.

cc/layers/painted_scrollbar_layer.cc

Index: cc/layers/painted_scrollbar_layer.cc
diff --git a/cc/layers/painted_scrollbar_layer.cc b/cc/layers/painted_scrollbar_layer.cc
index 71a37d48883f8f07d592ff561e288e344917ed65..493e74adb24769f1999e9ffd1e0a536ac839d927 100644
--- a/cc/layers/painted_scrollbar_layer.cc
+++ b/cc/layers/painted_scrollbar_layer.cc
@@ -244,7 +244,13 @@ UIResourceBitmap PaintedScrollbarLayer::RasterizeScrollbarPart(
   skbitmap.allocPixels();
 
   SkCanvas skcanvas(skbitmap);
-  skcanvas.translate(SkFloatToScalar(-rect.x()), SkFloatToScalar(-rect.y()));
+
+  // Skia will round to the nearest pixel on scaling, so we need to take that
+  // into account when translating back to the origin.
+  float adjustmentX = round(location_.x() * contents_scale_x());

[danakj, 2014/01/31 18:58:43]

Using location_ here looks wrong, the input |rect| is not always based on
location_, how about when it's the OriginThumbRect()?

[bokan, 2014/01/31 19:00:40]

yikes! You're right, I'll think about this some more...

+  float adjustmentY = round(location_.y() * contents_scale_y());
+  skcanvas.translate(SkFloatToScalar(-adjustmentX),
+      SkFloatToScalar(-adjustmentY));
   skcanvas.scale(SkFloatToScalar(contents_scale_x()),
                  SkFloatToScalar(contents_scale_y()));