cc: Don't track unnecessary checker-image data for UI compositor.

This change does a couple of things to ensure we don't track any
unnecessary data for checker-imaging:

1) During discardable image metadata generation, the decoding mode only
   needs to be tracked if the image is discardable.
2) We don't need to store any decoding mode metadata if checker-imaging
   is disabled.

R=ericrk@chromium.org

Bug: 1003886
Change-Id: I2802af3bcf69beb970b98a6c179032a72b588f2f
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1973152
Commit-Queue: Khushal <khushalsagar@chromium.org>
Reviewed-by: Eric Karl <ericrk@chromium.org>
Cr-Commit-Position: refs/heads/master@{#726685}

cc/paint/discardable_image_map.cc

@@ -346,15 +346,18 @@ class DiscardableImageGenerator {
     else
       rects->push_back(image_rect);
 
+    if (paint_image.IsLazyGenerated()) {
       auto decoding_mode_it = decoding_mode_map_.find(paint_image.stable_id());
       // Use the decoding mode if we don't have one yet, otherwise use the more
       // conservative one of the two existing ones.
       if (decoding_mode_it == decoding_mode_map_.end()) {
-      decoding_mode_map_[paint_image.stable_id()] = paint_image.decoding_mode();
+        decoding_mode_map_[paint_image.stable_id()] =
+            paint_image.decoding_mode();
       } else {
         decoding_mode_it->second = PaintImage::GetConservative(
             decoding_mode_it->second, paint_image.decoding_mode());
       }
+    }
 
     if (paint_image.ShouldAnimate()) {
       animated_images_metadata_.emplace_back(

cc/tiles/checker_image_tracker.cc

@@ -278,6 +278,9 @@ bool CheckerImageTracker::ShouldCheckerImage(const DrawImage& draw_image,
   if (!enable_checker_imaging_)
     return false;
 
+  if (!image.IsLazyGenerated())
+    return false;
+
   // If the image was invalidated on the current sync tree and the tile is
   // for the active tree, continue checkering it on the active tree to ensure
   // the image update is atomic for the frame.
@@ -455,6 +458,9 @@ void CheckerImageTracker::ScheduleNextImageDecode() {
 void CheckerImageTracker::UpdateImageDecodingHints(
     base::flat_map<PaintImage::Id, PaintImage::DecodingMode>
         decoding_mode_map) {
+  if (!enable_checker_imaging_)
+    return;
+
   // Merge the |decoding_mode_map| with our member map, keeping the more
   // conservative values.
   // TODO(vmpstr): Figure out if and how do we clear this value to ensure that

cc/trees/layer_tree_host_unittest.cc

@@ -8230,6 +8230,11 @@ MULTI_THREAD_TEST_F(
 
 class LayerTreeHostTestImageDecodingHints : public LayerTreeHostTest {
  public:
+  void InitializeSettings(LayerTreeSettings* settings) override {
+    LayerTreeHostTest::InitializeSettings(settings);
+    settings->enable_checker_imaging = true;
+  }
+
   void BeginTest() override { PostSetNeedsCommitToMainThread(); }
 
   void SetupTree() override {