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

cc/layers/viewport.cc

Index: cc/layers/viewport.cc
diff --git a/cc/layers/viewport.cc b/cc/layers/viewport.cc
index 80e711fd027db3979b9d2098ce5578ff6e911685..e53a716fbc935b46240e087fe82a2170219d1792 100644
--- a/cc/layers/viewport.cc
+++ b/cc/layers/viewport.cc
@@ -99,11 +99,11 @@ void Viewport::PinchUpdate(float magnify_delta, const gfx::Point& anchor) {
   gfx::Point adjusted_anchor = anchor + pinch_anchor_adjustment_;
   float page_scale = active_tree->current_page_scale_factor();
   gfx::PointF previous_scale_anchor =
-      gfx::ScalePoint(adjusted_anchor, 1.f / page_scale);
+      gfx::ScalePoint(gfx::PointF(adjusted_anchor), 1.f / page_scale);
   active_tree->SetPageScaleOnActiveTree(page_scale * magnify_delta);
   page_scale = active_tree->current_page_scale_factor();
   gfx::PointF new_scale_anchor =
-      gfx::ScalePoint(adjusted_anchor, 1.f / page_scale);
+      gfx::ScalePoint(gfx::PointF(adjusted_anchor), 1.f / page_scale);
   gfx::Vector2dF move = previous_scale_anchor - new_scale_anchor;
 
   // Scale back to viewport space since that's the coordinate space ScrollBy