Implement TracePathToObjectFrom helper for debugging.

R=verwaest@chromium.org

Review URL: https://chromiumcodereview.appspot.com/10823054

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@12222 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

src/heap.cc

@@ -6770,6 +6770,15 @@ void PathTracer::ProcessResults() {
 
 
 #ifdef DEBUG
+// Triggers a depth-first traversal of reachable objects from one
+// given root object and finds a path to a specific heap object and
+// prints it.
+void Heap::TracePathToObjectFrom(Object* target, Object* root) {
+  PathTracer tracer(target, PathTracer::FIND_ALL, VISIT_ALL);
+  tracer.VisitPointer(&root);
+}
+
+
 // Triggers a depth-first traversal of reachable objects from roots
 // and finds a path to a specific heap object and prints it.
 void Heap::TracePathToObject(Object* target) {

src/heap.h

@@ -1285,6 +1285,7 @@ class Heap {
     return disallow_allocation_failure_;
   }
 
+  void TracePathToObjectFrom(Object* target, Object* root);
   void TracePathToObject(Object* target);
   void TracePathToGlobal();
 #endif