No longer clean out main thread's heap for LSan's benefit.

third_party/WebKit/Source/platform/heap/ThreadState.cpp

 /*
  * Copyright (C) 2013 Google Inc. 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
@@ skipping 313 matching lines @@
   RELEASE_ASSERT(gcState() == NoGCScheduled);
 
   // Add pages to the orphaned page pool to ensure any global GCs from this
   // point on will not trace objects on this thread's arenas.
   cleanupPages();
 }
 
 void ThreadState::cleanupMainThread() {
   ASSERT(isMainThread());
 
-#if defined(LEAK_SANITIZER)
-  // See comment below, clear out most garbage before releasing static
-  // persistents should some of the finalizers depend on touching
-  // these persistents.
-  collectAllGarbage();
-#endif
-
   releaseStaticPersistentNodes();
 
-#if defined(LEAK_SANITIZER)
-  // If LSan is about to perform leak detection, after having released all
-  // the registered static Persistent<> root references to global caches
-  // that Blink keeps, follow up with a round of GCs to clear out all
-  // what they referred to.
-  //
-  // This is not needed for caches over non-Oilpan objects, as they're
-  // not scanned by LSan due to being held in non-global storage
-  // ("static" references inside functions/methods.)
-  collectAllGarbage();
-#endif
-
   // Finish sweeping before shutting down V8. Otherwise, some destructor
   // may access V8 and cause crashes.
   completeSweep();
 
   // It is unsafe to trigger GCs after this point because some
   // destructor may access already-detached V8 and cause crashes.
   // Also it is useless. So we forbid GCs.
   enterGCForbiddenScope();
 }
 
@@ skipping 1512 matching lines @@
     collectGarbage(BlinkGC::NoHeapPointersOnStack, BlinkGC::GCWithSweep,
                    BlinkGC::ForcedGC);
     size_t liveObjects = heap().heapStats().markedObjectSize();
     if (liveObjects == previousLiveObjects)
       break;
     previousLiveObjects = liveObjects;
   }
 }
 
 }  // namespace blink