Histogram to track missing and incomplete tiles

cc/trees/layer_tree_host_impl.cc

Index: cc/trees/layer_tree_host_impl.cc
diff --git a/cc/trees/layer_tree_host_impl.cc b/cc/trees/layer_tree_host_impl.cc
index de1e8ffcacd26e2befe65d392552ba699e0a7b75..3c15ebad53fc474b12bc1ff1458c8d83d9c66ba6 100644
--- a/cc/trees/layer_tree_host_impl.cc
+++ b/cc/trees/layer_tree_host_impl.cc
@@ -778,6 +778,9 @@ DrawResult LayerTreeHostImpl::CalculateRenderPasses(
 
   int layers_drawn = 0;
 
+  int num_missing_tiles = 0;
+  int num_incomplete_tiles = 0;
+
   const DrawMode draw_mode = GetDrawMode(output_surface_.get());
 
   LayerIteratorType end =
@@ -856,6 +859,7 @@ DrawResult LayerTreeHostImpl::CalculateRenderPasses(
         append_quads_data.approximated_visible_content_area);
 
     if (append_quads_data.num_missing_tiles) {
+      num_missing_tiles += append_quads_data.num_missing_tiles;
       bool layer_has_animating_transform =
           it->screen_space_transform_is_animating() ||
           it->draw_transform_is_animating();
@@ -863,7 +867,9 @@ DrawResult LayerTreeHostImpl::CalculateRenderPasses(
         draw_result = DRAW_ABORTED_CHECKERBOARD_ANIMATIONS;
     }
 
-    if (append_quads_data.had_incomplete_tile) {
+    if (append_quads_data.num_incomplete_tiles ||
+        append_quads_data.num_missing_tiles) {
+      num_incomplete_tiles += append_quads_data.num_incomplete_tiles;

[danakj, 2014/07/07 22:07:40]

maybe these += don't really fit inside these if blocks.. how about we just move
them both out below the if blocks. += 0 is a fine thing to do.

       frame->contains_incomplete_tile = true;
       if (active_tree()->RequiresHighResToDraw())
         draw_result = DRAW_ABORTED_MISSING_HIGH_RES_CONTENT;
@@ -914,6 +920,15 @@ DrawResult LayerTreeHostImpl::CalculateRenderPasses(
   // If we're making a frame to draw, it better have at least one render pass.
   DCHECK(!frame->render_passes.empty());
 
+  if (IsCurrentlyScrolling()) {
+    UMA_HISTOGRAM_COUNTS_100(
+        "Compositing.RenderPass.AppendQuadData.NumMissingTiles",
+        num_missing_tiles);
+    UMA_HISTOGRAM_COUNTS_100(
+        "Compositing.RenderPass.AppendQuadData.NumIncompleteTiles",
+        num_incomplete_tiles);
+  }
+
   // Should only have one render pass in resourceless software mode.
   if (output_surface_->ForcedDrawToSoftwareDevice())
     DCHECK_EQ(1u, frame->render_passes.size());