[heap] Add basic infrastructure for incremental wrapper tracing.

src/heap/incremental-marking.cc

Index: src/heap/incremental-marking.cc
diff --git a/src/heap/incremental-marking.cc b/src/heap/incremental-marking.cc
index 0c0f5b408ee5ae573dcdc8f533e7ad9d3987f620..0e4a568325969ef9b27e1161c2fbeaaf62f84460 100644
--- a/src/heap/incremental-marking.cc
+++ b/src/heap/incremental-marking.cc
@@ -1201,6 +1201,19 @@ intptr_t IncrementalMarking::Step(intptr_t allocated_bytes,
 
     if (state_ == MARKING) {
       bytes_processed = ProcessMarkingDeque(bytes_to_process);
+      if (FLAG_incremental_marking_wrappers &&
+          heap_->UsingEmbedderHeapTracer()) {
+        // This currently marks through all registered wrappers and does not
+        // respect bytes_to_priocess.

[Michael Lippautz, 2016/08/16 12:50:34]

nit: s/bytes_to_priocess/bytes_to_process/

+        // TODO(hpayer): Integrate incremental marking of wrappers into
+        // bytes_to_process logic.
+        heap_->mark_compact_collector()
+            ->RegisterWrappersWithEmbedderHeapTracer();
+        heap_->mark_compact_collector()->embedder_heap_tracer()->AdvanceTracing(
+            0,
+            EmbedderHeapTracer::AdvanceTracingActions(
+                EmbedderHeapTracer::ForceCompletionAction::FORCE_COMPLETION));
+      }
       if (heap_->mark_compact_collector()->marking_deque()->IsEmpty()) {
         if (completion == FORCE_COMPLETION ||
             IsIdleMarkingDelayCounterLimitReached()) {