cc: Outset image rects by 1 for the purposes of the rtree.

cc/playback/discardable_image_map.cc

Index: cc/playback/discardable_image_map.cc
diff --git a/cc/playback/discardable_image_map.cc b/cc/playback/discardable_image_map.cc
index 7e1abd6640bd83f8173b65cc565260b55e9c0a52..b5927f2b5ecadc4190746189be49aec65cf377ae 100644
--- a/cc/playback/discardable_image_map.cc
+++ b/cc/playback/discardable_image_map.cc
@@ -172,6 +172,7 @@ class DiscardableImagesMetadataCanvas : public SkNWayCanvas {
         return false;
       *paint_bounds = paint.computeFastBounds(*paint_bounds, paint_bounds);
     }
+
     return true;
   }
 
@@ -202,6 +203,18 @@ class DiscardableImagesMetadataCanvas : public SkNWayCanvas {
     src_rect.roundOut(&src_irect);
     gfx::Rect image_rect = SafeClampPaintRectToSize(paint_rect, canvas_size_);
 
+    // During raster, we use the device clip bounds on the canvas, which outsets
+    // the actual clip by 1 due to the possibility of antialiasing. Account for
+    // this here by outsetting the image rect by 1. Note that this only affects
+    // queries into the rtree, which will now return images that only touch the
+    // bounds of the query rect.
+    //
+    // Note that it's not sufficient for us to inset the device clip bounds at
+    // raster time, since we might be sending a larger-than-one-item display
+    // item to skia, which means that skia will internally determine whether to
+    // raster the picture (using device clip bounds that are outset).
+    image_rect.Inset(-1, -1);
+
     (*image_id_to_rect_)[image->uniqueID()].Union(image_rect);
     image_set_->push_back(std::make_pair(
         DrawImage(std::move(image), src_irect, filter_quality, matrix),