CC: Have GPU-raster tiles exactly match the viewport.

cc/layers/picture_layer_impl_unittest.cc

Index: cc/layers/picture_layer_impl_unittest.cc
diff --git a/cc/layers/picture_layer_impl_unittest.cc b/cc/layers/picture_layer_impl_unittest.cc
index b25a9d504aa365c650ad3814006ec56405ec754b..5d8026872de877f9905c6bb0fe36fa9c99169b3a 100644
--- a/cc/layers/picture_layer_impl_unittest.cc
+++ b/cc/layers/picture_layer_impl_unittest.cc
@@ -4408,22 +4408,22 @@ TEST_F(TileSizeTest, TileSizes) {
   EXPECT_EQ(result.width(), 200);
   EXPECT_EQ(result.height(), 200);
 
-  host_impl_.SetUseGpuRasterization(true);
-
   // Gpu-rasterization uses 25% viewport-height tiles.
+  // The +2's below are for border texels.
+  host_impl_.SetUseGpuRasterization(true);
   result = layer->CalculateTileSize(gfx::Size(10000, 10000));
   EXPECT_EQ(result.width(), 1000);
-  EXPECT_EQ(result.height(), 250);
+  EXPECT_EQ(result.height(), 250 + 2);
 
   // Clamp and round-up, when smaller than viewport.
   result = layer->CalculateTileSize(gfx::Size(831, 10000));
   EXPECT_EQ(result.width(), 832);
-  EXPECT_EQ(result.height(), 250);
+  EXPECT_EQ(result.height(), 250 + 2);
 
   // Tile-height doubles to 50% when width shrinks to <= 50%.

[enne (OOO), 2014/10/10 00:06:05]

For what it's worth, I think this "viewport / 4" makes a lot of sense for long
scrollable layers.  But it doesn't make really all that much sense for most
other layers that (currently) get created.

I guess I'm trying to say this relative 50% is kind of weird and maybe should be
absolute.  Would it make sense to have a "max untiled size" for ganesh as well,
so that small layers don't get divided up by viewport size too?

   result = layer->CalculateTileSize(gfx::Size(447, 10000));
   EXPECT_EQ(result.width(), 448);
-  EXPECT_EQ(result.height(), 500);
+  EXPECT_EQ(result.height(), 500 + 2);
 
   // Largest layer is 50% of viewport width (rounded up), and
   // 50% of viewport in height.
@@ -4432,7 +4432,7 @@ TEST_F(TileSizeTest, TileSizes) {
   EXPECT_EQ(result.height(), 448);
   result = layer->CalculateTileSize(gfx::Size(500, 499));
   EXPECT_EQ(result.width(), 512);
-  EXPECT_EQ(result.height(), 500);
+  EXPECT_EQ(result.height(), 500 + 2);
 }
 
 }  // namespace