Added compositing_reason_ids to the Layer trace data

The DevTools Performance Timeline tool with 'Advanced paint instrumentation' enabled captures layer trace events, which includes compositing reasons. This change adds compositing_reason_ids to the trace information, so that we can localize the compositing reasons in the client (i.e. DevTools frontend).

Bug: 946860
Change-Id: Ibb9b655c739947898b857489d5f8d727a40ef19b
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2031528Reviewed-by: Mandy Chen <mandy.chen@microsoft.com>
Reviewed-by: Philip Rogers <pdr@chromium.org>
Commit-Queue: Lorne Mitchell <lomitch@microsoft.com>
Cr-Commit-Position: refs/heads/master@{#736995}

cc/layers/layer_impl.cc

@@ -781,6 +781,13 @@ void LayerImpl::AsValueInto(base::trace_event::TracedValue* state) const {
       state->EndArray();
     }
 
+    if (debug_info_->compositing_reason_ids.size()) {
+      state->BeginArray("compositing_reason_ids");
+      for (const char* reason_id : debug_info_->compositing_reason_ids)
+        state->AppendString(reason_id);
+      state->EndArray();
+    }
+
     if (debug_info_->invalidations.size()) {
       state->BeginArray("annotated_invalidation_rects");
       for (auto& invalidation : debug_info_->invalidations) {