Introduce a flag for tracing retaining path in GC.

src/heap/mark-compact.cc

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "src/v8.h"
 
 #include "src/base/atomicops.h"
 #include "src/base/bits.h"
 #include "src/code-stubs.h"
 #include "src/compilation-cache.h"
@@ skipping 2076 matching lines @@
 
 
 // Mark all objects reachable (transitively) from objects on the marking
 // stack including references only considered in the atomic marking pause.
 void MarkCompactCollector::ProcessEphemeralMarking(
     ObjectVisitor* visitor, bool only_process_harmony_weak_collections) {
   bool work_to_do = true;
   DCHECK(marking_deque_.IsEmpty() && !marking_deque_.overflowed());
   while (work_to_do) {
     if (!only_process_harmony_weak_collections) {
+#ifdef TRACE_RETAINING_PATH
+      heap()->SetCurrentRootRetainer(std::string("[weak global handles]"));
+#endif
       isolate()->global_handles()->IterateObjectGroups(
           visitor, &IsUnmarkedHeapObjectWithHeap);
       MarkImplicitRefGroups();
     }
+#ifdef TRACE_RETAINING_PATH
+    heap()->SetCurrentRootRetainer(std::string("[weak harmony collections]"));
+#endif
     ProcessWeakCollections();
     work_to_do = !marking_deque_.IsEmpty();
     ProcessMarkingDeque();
   }
 }
 
 
 void MarkCompactCollector::ProcessTopOptimizedFrame(ObjectVisitor* visitor) {
+#ifdef TRACE_RETAINING_PATH
+  heap()->SetCurrentRootRetainer(std::string("[top optimized frame]"));
+#endif
   for (StackFrameIterator it(isolate(), isolate()->thread_local_top());
        !it.done(); it.Advance()) {
     if (it.frame()->type() == StackFrame::JAVA_SCRIPT) {
       return;
     }
     if (it.frame()->type() == StackFrame::OPTIMIZED) {
       Code* code = it.frame()->LookupCode();
       if (!code->CanDeoptAt(it.frame()->pc())) {
         code->CodeIterateBody(visitor);
       }
@@ skipping 2286 matching lines @@
 
 void SlotsBufferAllocator::DeallocateChain(SlotsBuffer** buffer_address) {
   SlotsBuffer* buffer = *buffer_address;
   while (buffer != NULL) {
     SlotsBuffer* next_buffer = buffer->next();
     DeallocateBuffer(buffer);
     buffer = next_buffer;
   }
   *buffer_address = NULL;
 }
+
+
+#ifdef TRACE_RETAINING_PATH
+void MarkingDeque::AddRetainedObject(HeapObject* obj) {
+  obj->GetHeap()->AddRetainedObject(obj);
+}
+#endif
 }
 }  // namespace v8::internal