cc: Only clear edge pixels that fall inside the canvas_playback_rect

When we raster a tile at scale, edge pixels may not be fully covered
by the recording, so we clear them to the background color. When
partially rastering the tile, though, we only want to clear edge pixels
that are inside the dirty rect, since we won't re-raster stuff outside.

R=enne, vmpstr
BUG=499245
CQ_INCLUDE_TRYBOTS=tryserver.blink:linux_blink_rel

Review URL: https://codereview.chromium.org/1182533002

Cr-Commit-Position: refs/heads/master@{#334018}

1 files changed, 4 insertions, 3 deletions

diff --git a/cc/playback/display_list_raster_source_unittest.cc b/cc/playback/display_list_raster_source_unittest.cc
index e41bc64..1827d71 100644
--- a/cc/playback/display_list_raster_source_unittest.cc
+++ b/cc/playback/display_list_raster_source_unittest.cc
@@ -395,8 +395,9 @@ TEST(DisplayListRasterSourceTest, RasterPartialContents) {
   raster = DisplayListRasterSource::CreateFromDisplayListRecordingSource(
       recording_source.get(), false);
 
-  // We're going to playback from "everything is black" into a smaller area.
-  playback_rect.Inset(1, 2);
+  // We're going to playback from "everything is black" into a smaller area,
+  // that touches the edge pixels of the recording.
+  playback_rect.Inset(1, 2, 0, 1);
   raster->PlaybackToCanvas(&canvas, raster_full_rect, playback_rect,
                            contents_scale);
 
@@ -405,8 +406,8 @@ TEST(DisplayListRasterSourceTest, RasterPartialContents) {
   int num_white = 0;
   for (int i = 0; i < bitmap.width(); ++i) {
     for (int j = 0; j < bitmap.height(); ++j) {
-      SCOPED_TRACE(i);
       SCOPED_TRACE(j);
+      SCOPED_TRACE(i);
       bool expect_black = playback_rect.Contains(i, j);
       if (expect_black) {
         EXPECT_EQ(255u, SkColorGetA(pixels[i + j * bitmap.width()]));