Fix UpdateTilePriorities viewport in Android WebView.

This patch fixes the tile management viewport to be the on-screen-visible
rect for the last hardware draw.  There are two problems I needed to solve:

1) Suppress UpdateTilePriorities from happening when the last draw was a
software draw, which is specified by the new
"viewport_valid_for_tile_management" bool.

2) In some cases, the clip rect is smaller than the WebView's visible
viewport -- for example when the Android Browser progress bar is forcing
redraws, the clip is only a small area at the top of the screen.  I
switched to using the visible viewport for UpdateDrawProperties +
glViewport, and introduce a separate "DeviceClip" to override glScissor.
(It's necessary to make the change at this level, rather than directly
plumbing the visible viewport to UpdateTilePriorities, because
UpdateTilePriorities also makes use of outputs from the draw properties
calculation.)

I also cleaned up all uses of device_viewport_size() to call DrawViewportSize()
instead, with the sole exception of UnscaledScrollableViewportSize() which
should continue to use the main-thread device_viewport_size_ in all cases
(because that's the viewport for scrolling, not drawing).

New tests: PictureLayerImplTest.SuppressUpdateTilePriorities,
           ExternalStencilPixelTest.DeviceClip

NOTRY=true
BUG=232844

Review URL: https://chromiumcodereview.appspot.com/23171014

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@221321 0039d316-1c4b-4281-b951-d872f2087c98

1 files changed, 5 insertions, 1 deletions

diff --git a/cc/test/pixel_test_output_surface.cc b/cc/test/pixel_test_output_surface.cc
index 9a4d66a..ffc3d26c 100644
--- a/cc/test/pixel_test_output_surface.cc
+++ b/cc/test/pixel_test_output_surface.cc
@@ -15,7 +15,11 @@ void PixelTestOutputSurface::Reshape(gfx::Size size, float scale_factor) {
   OutputSurface::Reshape(expanded_size, scale_factor);
 
   gfx::Rect offset_viewport = gfx::Rect(size) + viewport_offset_;
-  SetExternalDrawConstraints(gfx::Transform(), offset_viewport);
+  gfx::Rect offset_clip = device_clip_.IsEmpty()
+                              ? offset_viewport
+                              : device_clip_ + viewport_offset_;
+  SetExternalDrawConstraints(
+      gfx::Transform(), offset_viewport, offset_clip, true);
 }
 
 }  // namespace cc