gfx: Make conversions from Size to SizeF be explicit.

cc/playback/picture_pile_impl_unittest.cc

Index: cc/playback/picture_pile_impl_unittest.cc
diff --git a/cc/playback/picture_pile_impl_unittest.cc b/cc/playback/picture_pile_impl_unittest.cc
index 3931f8dd4239b6f80f73e79a41ee15282914714c..f0b95ef08f901f6e82765538d920d179894bf1ef 100644
--- a/cc/playback/picture_pile_impl_unittest.cc
+++ b/cc/playback/picture_pile_impl_unittest.cc
@@ -292,8 +292,8 @@ TEST(PicturePileImplTest, RasterFullContents) {
   scoped_refptr<FakePicturePileImpl> pile =
       FakePicturePileImpl::CreateFromPile(recording_source.get(), nullptr);
 
-  gfx::Size content_bounds(
-      gfx::ToCeiledSize(gfx::ScaleSize(layer_bounds, contents_scale)));
+  gfx::Size content_bounds =
+      gfx::ScaleToCeiledSize(layer_bounds, contents_scale);
 
   // Simulate drawing into different tiles at different offsets.
   int step_x = std::ceil(content_bounds.width() / raster_divisions);
@@ -351,8 +351,8 @@ TEST(PicturePileImpl, RasterContentsTransparent) {
 
   scoped_refptr<FakePicturePileImpl> pile =
       FakePicturePileImpl::CreateFromPile(recording_source.get(), nullptr);
-  gfx::Size content_bounds(
-      gfx::ToCeiledSize(gfx::ScaleSize(layer_bounds, contents_scale)));
+  gfx::Size content_bounds =
+      gfx::ScaleToCeiledSize(layer_bounds, contents_scale);
 
   gfx::Rect canvas_rect(content_bounds);
   canvas_rect.Inset(0, 0, -1, -1);
@@ -401,8 +401,8 @@ TEST_P(OverlapTest, NoOverlap) {
 
   scoped_refptr<FakePicturePileImpl> pile =
       FakePicturePileImpl::CreateFromPile(recording_source.get(), nullptr);
-  gfx::Size content_bounds(
-      gfx::ToCeiledSize(gfx::ScaleSize(layer_bounds, contents_scale)));
+  gfx::Size content_bounds =
+      gfx::ScaleToCeiledSize(layer_bounds, contents_scale);
 
   SkBitmap bitmap;
   bitmap.allocN32Pixels(content_bounds.width(), content_bounds.height());