Scale the ALPHA_THRESHOLD filter's region based on the device scale factor.

cc/base/math_util.cc

Index: cc/base/math_util.cc
diff --git a/cc/base/math_util.cc b/cc/base/math_util.cc
index a619b50698b4c536ec3cd9542b60b67e5349b4c3..4f5c44208be60444d6505ca14e2d0c14386ea303 100644
--- a/cc/base/math_util.cc
+++ b/cc/base/math_util.cc
@@ -606,6 +606,13 @@ scoped_ptr<base::Value> MathUtil::AsValue(const gfx::Vector2d& v) {
   return res.PassAs<base::Value>();
 }
 
+scoped_ptr<base::Value> MathUtil::AsValue(const gfx::Vector2dF& v) {
+  scoped_ptr<base::ListValue> res(new base::ListValue());
+  res->AppendDouble(v.x());
+  res->AppendDouble(v.y());
+  return res.PassAs<base::Value>();
+}
+
 scoped_ptr<base::Value> MathUtil::AsValue(const gfx::QuadF& q) {
   scoped_ptr<base::ListValue> res(new base::ListValue());
   res->AppendDouble(q.p1().x());