cc: Move draw params from SetExternalDrawConstraints to OnDraw

cc/test/layer_tree_pixel_test.cc

Index: cc/test/layer_tree_pixel_test.cc
diff --git a/cc/test/layer_tree_pixel_test.cc b/cc/test/layer_tree_pixel_test.cc
index f29ae8669f657a8b1e367388227132fc5173dec2..77e946ab582c06d1a3168a6a09e3e98ab86573c8 100644
--- a/cc/test/layer_tree_pixel_test.cc
+++ b/cc/test/layer_tree_pixel_test.cc
@@ -74,14 +74,7 @@ void LayerTreePixelTest::WillCommitCompleteOnThread(LayerTreeHostImpl* impl) {
   EXPECT_EQ(gfx::Point().ToString(), viewport.origin().ToString());
   // Be that influence!
   viewport += gfx::Vector2d(20, 10);
-  bool resourceless_software_draw = false;
-  gfx::Transform identity = gfx::Transform();
-  impl->SetExternalDrawConstraints(identity,
-                                   viewport,
-                                   viewport,
-                                   viewport,
-                                   identity,
-                                   resourceless_software_draw);
+  impl->SetExternalViewportForTesting(viewport);

[boliu, 2015/12/15 23:46:45]

This one I'm confused. Not sure where this magic translate(20,10) comes from or
why it's needed.

Removing this only breaks two pixel tests:
ImageScaledBackgroundFilter.ImageFilterScaled_GL
LayerTreeHostFiltersPixelTest.BackgroundFilterBlurOffAxis

Resulting image in both tests differs only by 11 pixels. They visually look the
same, so it's not a shift of the whole image or anything. Should I just
rebaseline these and remove this?

[danakj, 2015/12/16 23:57:53]

Hrm, that is very weird. Pretty sure this was meant to move the contents of the
test outputs or something.. well, I think the right thing to test for a pixel
test wrt to this would be to call DrawFrame with a viewport rect of choice
directly with other pixel tests, and not for these layer tree tests, so ok.

   EXPECT_EQ(viewport.ToString(), impl->DeviceViewport().ToString());
 }