Check if priority actually changed in Tile::SetPriority()

To prevent unnecessary TileManager::WillModifyTilePriority() calls which
blocks ActivatePendingTree(), commits and the whole event queue.

BUG=181708


Review URL: https://chromiumcodereview.appspot.com/12912008

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@189543 0039d316-1c4b-4281-b951-d872f2087c98

2 files changed, 17 insertions, 0 deletions

diff --git a/cc/resources/tile.cc b/cc/resources/tile.cc
index 48f3ae7..f29baf6 100644
--- a/cc/resources/tile.cc
+++ b/cc/resources/tile.cc
@@ -46,6 +46,9 @@ scoped_ptr<base::Value> Tile::AsValue() const {
 }
 
 void Tile::SetPriority(WhichTree tree, const TilePriority& priority) {
+  if (priority_[tree] == priority)
+    return;
+
   tile_manager_->WillModifyTilePriority(this, tree, priority);
   priority_[tree] = priority;
 }
diff --git a/cc/resources/tile_priority.h b/cc/resources/tile_priority.h
index c998624..a9558ef 100644
--- a/cc/resources/tile_priority.h
+++ b/cc/resources/tile_priority.h
@@ -122,6 +122,20 @@ struct CC_EXPORT TilePriority {
                                         float time_delta,
                                         const gfx::RectF& target_bounds);
 
+  bool operator ==(const TilePriority& other) const {
+    if (is_live != other.is_live) return false;
+    if (!is_live) return true;  // All non-live priorities are the same.
+    return resolution == other.resolution &&
+        time_to_visible_in_seconds == other.time_to_visible_in_seconds &&
+        distance_to_visible_in_pixels == other.distance_to_visible_in_pixels;
+    // No need to compare current_screen_quad which is for debug only and
+    // never changes by itself.
+  }
+
+  bool operator !=(const TilePriority& other) const {
+    return !(*this == other);
+  }
+
   // If a tile is not live, then all other fields are invalid.
   bool is_live;
   TileResolution resolution;