[heap] Add timer scopes to process weak cells and clear non-live references.

BUG=

Review URL: https://codereview.chromium.org/1345273004

Cr-Commit-Position: refs/heads/master@{#30848}

src/heap/gc-tracer.cc

@@ -450,6 +450,9 @@ void GCTracer::PrintNVP() const {
              current_.scopes[Scope::MC_WEAKCOLLECTION_CLEAR]);
       PrintF("weakcollection_abort=%.1f ",
              current_.scopes[Scope::MC_WEAKCOLLECTION_ABORT]);
+      PrintF("weakcells=%.1f ", current_.scopes[Scope::MC_WEAKCELL]);
+      PrintF("nonlive_refs=%.1f ",
+             current_.scopes[Scope::MC_NONLIVEREFERENCES]);
 
       PrintF("steps_count=%d ", current_.incremental_marking_steps);
       PrintF("steps_took=%.1f ", current_.incremental_marking_duration);

src/heap/gc-tracer.h

@@ -117,6 +117,8 @@ class GCTracer {
       MC_WEAKCOLLECTION_PROCESS,
       MC_WEAKCOLLECTION_CLEAR,
       MC_WEAKCOLLECTION_ABORT,
+      MC_WEAKCELL,
+      MC_NONLIVEREFERENCES,
       MC_FLUSH_CODE,
       SCAVENGER_CODE_FLUSH_CANDIDATES,
       SCAVENGER_OBJECT_GROUPS,

src/heap/mark-compact.cc

@@ -2216,6 +2216,8 @@ void MarkCompactCollector::AfterMarking() {
 
 
 void MarkCompactCollector::ClearNonLiveReferences() {
+  GCTracer::Scope gc_scope(heap()->tracer(),
+                           GCTracer::Scope::MC_NONLIVEREFERENCES);
   // Iterate over the map space, setting map transitions that go from
   // a marked map to an unmarked map to null transitions.  This action
   // is carried out only on maps of JSObjects and related subtypes.
@@ -2509,6 +2511,7 @@ void MarkCompactCollector::AbortWeakCollections() {
 
 
 void MarkCompactCollector::ProcessAndClearWeakCells() {
+  GCTracer::Scope gc_scope(heap()->tracer(), GCTracer::Scope::MC_WEAKCELL);
   Object* weak_cell_obj = heap()->encountered_weak_cells();
   while (weak_cell_obj != Smi::FromInt(0)) {
     WeakCell* weak_cell = reinterpret_cast<WeakCell*>(weak_cell_obj);