Fixing tile grid size used by cc:Picture to make it respect current tile configuration

cc/picture_layer.cc

Index: cc/picture_layer.cc
diff --git a/cc/picture_layer.cc b/cc/picture_layer.cc
index b9ce65a50240b32e79e5b2e4c94c09d4e4ca418c..b7de08990863a50aec68198fd2b10e6398695418 100644
--- a/cc/picture_layer.cc
+++ b/cc/picture_layer.cc
@@ -46,8 +46,16 @@ void PictureLayer::pushPropertiesTo(LayerImpl* base_layer) {
 
 void PictureLayer::setLayerTreeHost(LayerTreeHost* host) {
   Layer::setLayerTreeHost(host);
-  if (host)
-      pile_->SetMinContentsScale(host->settings().minimumContentsScale);
+  if (host) {
+    pile_->SetMinContentsScale(host->settings().minimumContentsScale);
+    gfx::Size tile_size = host->settings().defaultTileSize;
+    float scale = host->deviceScaleFactor();
+    // The -2 is to account for border pixels, +0.5 is for rounding

[enne (OOO), 2013/02/15 20:39:50]

This math doesn't look right.  The border texels are not affected by scale, and
everything is rounded up, not rounded to the nearest int.  In other words,
ceil(width / scale) - 2.

+    gfx::Size tile_grid_stride(
+        static_cast<int>((tile_size.width() - 2) / scale + 0.5f),
+        static_cast<int>((tile_size.height() - 2) / scale + 0.5f));
+    pile_->SetTileGridStride(tile_grid_stride);
+  }
 }
 
 void PictureLayer::setNeedsDisplayRect(const gfx::RectF& layer_rect) {