Oilpan: Validate pointers stored in Persistent

Source/platform/heap/HeapTest.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 3503 matching lines @@
         Persistent<WithWeakMember> h5;
         Heap::collectGarbage(ThreadState::NoHeapPointersOnStack, ThreadState::GCWithSweep, Heap::ForcedGC);
         ASSERT_EQ(1u, Bar::s_live); // h1 is live.
         {
             Bar* h2 = Bar::create();
             Bar* h3 = Bar::create();
             h4 = Weak::create(h2, h3);
             h5 = WithWeakMember::create(h2, h3);
             Heap::collectGarbage(ThreadState::HeapPointersOnStack, ThreadState::GCWithSweep, Heap::ForcedGC);
             EXPECT_EQ(5u, Bar::s_live); // The on-stack pointer keeps h3 alive.
+            EXPECT_FALSE(h3->hasBeenFinalized());

[haraken, 2015/05/26 06:50:13]

OK, now I finally found the cause of the failure on win_rel_bot.

Without having this line, there is no user of h3 after the line 3519. So the
compiler can optimize out the h3 pointer from the stack. Then the GC can collect
the h3 and thus crash at the line 3523. Adding the line fixes the crash.

[Yuta Kitamura, 2015/05/26 09:26:29]

"volatile" can be used, maybe?

             EXPECT_TRUE(h4->strongIsThere());
             EXPECT_TRUE(h4->weakIsThere());
             EXPECT_TRUE(h5->strongIsThere());
             EXPECT_TRUE(h5->weakIsThere());
         }
         // h3 is collected, weak pointers from h4 and h5 don't keep it alive.
         Heap::collectGarbage(ThreadState::NoHeapPointersOnStack, ThreadState::GCWithSweep, Heap::ForcedGC);
         EXPECT_EQ(4u, Bar::s_live);
         EXPECT_TRUE(h4->strongIsThere());
         EXPECT_FALSE(h4->weakIsThere()); // h3 is gone from weak pointer.
@@ skipping 2577 matching lines @@
 {
     Persistent<ClassWithMember> object = ClassWithMember::create();
     EXPECT_EQ(0, object->traceCount());
     TestMixinAllocatingObject* mixin = TestMixinAllocatingObject::create(object.get());
     EXPECT_TRUE(mixin);
     EXPECT_GT(object->traceCount(), 0);
     EXPECT_GT(mixin->traceCount(), 0);
 }
 
 } // namespace blink