[heap] Do not invoke GC to make heap iterable.

test/cctest/test-heap-profiler.cc

 // Copyright 2011 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 687 matching lines @@
   const v8::HeapSnapshot* snapshot1 = heap_profiler->TakeHeapSnapshot();
   CHECK(ValidateSnapshot(snapshot1));
   v8::SnapshotObjectId maxId1 = snapshot1->GetMaxSnapshotJSObjectId();
 
   CompileRun(
       "for (var i = 0; i < 10000; ++i)\n"
       "  a[i] = new A();\n");
   CcTest::heap()->CollectAllGarbage();
 
   const v8::HeapSnapshot* snapshot2 = heap_profiler->TakeHeapSnapshot();
-  CHECK(ValidateSnapshot(snapshot2));
   const v8::HeapGraphNode* global2 = GetGlobalObject(snapshot2);
 
   const v8::HeapGraphNode* array_node =
       GetProperty(global2, v8::HeapGraphEdge::kProperty, "a");
   CHECK(array_node);
   int wrong_count = 0;
   for (int i = 0, count = array_node->GetChildrenCount(); i < count; ++i) {
     const v8::HeapGraphEdge* prop = array_node->GetChild(i);
     if (prop->GetType() != v8::HeapGraphEdge::kElement)
       continue;
@@ skipping 2330 matching lines @@
       "      a[i] = i;\n"
       "  for (var i = 0; i < 3; ++i)\n"
       "      a.shift();\n"
       "}\n");
 
   CcTest::heap()->CollectGarbage(v8::internal::NEW_SPACE);
   // Should not crash.
 
   heap_profiler->StopSamplingHeapProfiler();
 }