[heap] Introduce phase for marking wrappers

Introduces a phase for marking wrappers in the atomic pause. The phase
is opportunistic in a sense that it may no catch all wrappers. E.g.
there may be wrappers discovered only after processing ephemerons.

Bug: chromium:843903
Change-Id: Ic55fdcb37e3ff44156e4eca4c1c95919fc3fcd1d
Reviewed-on: https://chromium-review.googlesource.com/1166835Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Commit-Queue: Michael Lippautz <mlippautz@chromium.org>
Cr-Commit-Position: refs/heads/master@{#54962}

src/heap-symbols.h

@@ -351,6 +351,7 @@
   F(MC_MARK_WEAK_CLOSURE_WEAK_HANDLES)               \
   F(MC_MARK_WEAK_CLOSURE_WEAK_ROOTS)                 \
   F(MC_MARK_WEAK_CLOSURE_HARMONY)                    \
+  F(MC_MARK_WRAPPERS)                                \
   F(MC_MARK_WRAPPER_EPILOGUE)                        \
   F(MC_MARK_WRAPPER_PROLOGUE)                        \
   F(MC_MARK_WRAPPER_TRACING)                         \

src/heap/mark-compact.cc

@@ -1784,6 +1784,18 @@ void MarkCompactCollector::MarkLiveObjects() {
 
     DCHECK(marking_worklist()->IsEmpty());
 
+    // Mark objects reachable through the embedder heap. This phase is
+    // opportunistic as it may not discover graphs that are only reachable
+    // through ephemerons.
+    {
+      TRACE_GC(heap()->tracer(), GCTracer::Scope::MC_MARK_WRAPPERS);
+      while (!heap_->local_embedder_heap_tracer()->IsRemoteTracingDone()) {
+        PerformWrapperTracing();
+        ProcessMarkingWorklist();
+      }
+      DCHECK(marking_worklist()->IsEmpty());
+    }
+
     // The objects reachable from the roots are marked, yet unreachable objects
     // are unmarked. Mark objects reachable due to embedder heap tracing or
     // harmony weak maps.