Fix performance regression of heap snapshot generator that was

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 475 matching lines @@
 }
 
 
 void CheckSimdSnapshot(const char* program, const char* var_name) {
   i::FLAG_harmony_simd = true;
   LocalContext env;
   v8::HandleScope scope(env->GetIsolate());
   v8::HeapProfiler* heap_profiler = env->GetIsolate()->GetHeapProfiler();
 
   CompileRun(program);
+  // The TakeHeapSnapshot function does not do enough GCs to ensure
+  // that all garbage is collected. We perform addition GC here
+  // to reclaim a floating AllocationSite and to fix the following failure:
+  // # Check failed: ValidateSnapshot(snapshot).
+  // Stdout:
+  //     28 @ 13523   entry with no retainer: /hidden/ system / AllocationSite
+  //     44 @   767    $map: /hidden/ system / Map
+  //     44 @    59      $map: /hidden/ system / Map
+  CcTest::heap()->CollectAllGarbage();
+
   const v8::HeapSnapshot* snapshot = heap_profiler->TakeHeapSnapshot();
   CHECK(ValidateSnapshot(snapshot));
   const v8::HeapGraphNode* global = GetGlobalObject(snapshot);
   const v8::HeapGraphNode* var =
       GetProperty(global, v8::HeapGraphEdge::kProperty, var_name);
   CHECK(var);
   CHECK_EQ(var->GetType(), v8::HeapGraphNode::kSimdValue);
 }
 
 
@@ skipping 2544 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();
 }