Chromium -> Mojo roll.

cc/debug/frame_viewer_instrumentation.cc

Index: cc/debug/frame_viewer_instrumentation.cc
diff --git a/cc/debug/frame_viewer_instrumentation.cc b/cc/debug/frame_viewer_instrumentation.cc
index 53c155166b8b3f5f21549d12e88e226945b606d8..226cc88e1185da138a9eadc26eac2272ccbf586c 100644
--- a/cc/debug/frame_viewer_instrumentation.cc
+++ b/cc/debug/frame_viewer_instrumentation.cc
@@ -6,6 +6,12 @@
 
 namespace cc {
 namespace frame_viewer_instrumentation {
+
+const char kCategoryLayerTree[] =
+    TRACE_DISABLED_BY_DEFAULT("cc.debug") ","
+    TRACE_DISABLED_BY_DEFAULT("cc.debug.quads") ","
+    TRACE_DISABLED_BY_DEFAULT("devtools.timeline.layers");
+
 namespace {
 
 const char kCategory[] = "cc," TRACE_DISABLED_BY_DEFAULT("devtools.timeline");
@@ -60,5 +66,11 @@ ScopedRasterTask::~ScopedRasterTask() {
   TRACE_EVENT_END0(kCategory, kRasterTask);
 }
 
+bool IsTracingLayerTreeSnapshots() {
+  bool category_enabled;
+  TRACE_EVENT_CATEGORY_GROUP_ENABLED(kCategoryLayerTree, &category_enabled);
+  return category_enabled;
+}
+
 }  // namespace frame_viewer_instrumentation
 }  // namespace cc