gfx: Make conversions from gfx::Point to PointF explicit.

cc/layers/layer_iterator_unittest.cc

Index: cc/layers/layer_iterator_unittest.cc
diff --git a/cc/layers/layer_iterator_unittest.cc b/cc/layers/layer_iterator_unittest.cc
index 01815f9b36ceca8eb59061ecf8383476ac8285ca..ee429a29bb8308f3288d88b31df58bed35af55f6 100644
--- a/cc/layers/layer_iterator_unittest.cc
+++ b/cc/layers/layer_iterator_unittest.cc
@@ -40,7 +40,7 @@ class TestLayerImpl : public LayerImpl {
         count_representing_contributing_surface_(-1),
         count_representing_itself_(-1) {
     SetBounds(gfx::Size(100, 100));
-    SetPosition(gfx::Point());
+    SetPosition(gfx::PointF());
     SetDrawsContent(true);
   }
 };