[oilpan]: Make thread shutdown more robust.

Source/platform/heap/HeapTest.cpp

 /*
  * Copyright (C) 2013 Google Inc. All rights reserved.

[haraken, 2014/07/08 05:44:51]

I understand that it's a pain to add tests, but we might want to have tests for
this change because a lot of non-trivial things happen around the orphaned
pages.

[wibling-chromium, 2014/07/08 13:39:47]

I will try to cook something up. It might be in a follow-up change if that's
okay with you.

[haraken, 2014/07/09 05:17:48]

Actually I want to have tests on this CL. Once this CL lands, the orphaned page
logic starts running in production builds. It's a bit scary to land the
complicated logic without having tests.

[wibling-chromium, 2014/07/09 10:32:30]

Okay. That said we do have all the layout tests which should exercise 
this. To verify I also changed 

WorkerThreadableWebSocketChannel::Peer::destroy

to not clear the keepAlive and verified both in debugger and without that the
code is working.

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@@ skipping 1677 matching lines @@
     Heap::collectGarbage(ThreadState::NoHeapPointersOnStack);
     EXPECT_EQ(2, HeapTestSubClass::s_destructorCalls);
     EXPECT_EQ(3, HeapTestSuperClass::s_destructorCalls);
 }
 
 TEST(HeapTest, TypedHeapSanity)
 {
     // We use TraceCounter for allocating an object on the general heap.
     Persistent<TraceCounter> generalHeapObject = TraceCounter::create();
     Persistent<TestTypedHeapClass> typedHeapObject = TestTypedHeapClass::create();
-    EXPECT_NE(pageHeaderAddress(reinterpret_cast<Address>(generalHeapObject.get())),
-        pageHeaderAddress(reinterpret_cast<Address>(typedHeapObject.get())));
+    EXPECT_NE(pageHeaderFromObject(generalHeapObject.get()),
+        pageHeaderFromObject(typedHeapObject.get()));
 }
 
 TEST(HeapTest, NoAllocation)
 {
     EXPECT_TRUE(ThreadState::current()->isAllocationAllowed());
     {
         // Disallow allocation
         NoAllocationScope<AnyThread> noAllocationScope;
         EXPECT_FALSE(ThreadState::current()->isAllocationAllowed());
     }
@@ skipping 2866 matching lines @@
     Heap::collectGarbage(ThreadState::NoHeapPointersOnStack);
     EXPECT_EQ(1u, map->size());
     EXPECT_EQ(lifeObject, map->get(lifeObject)->link());
     lifeObject.clear(); // Despite its name.
     Heap::collectGarbage(ThreadState::NoHeapPointersOnStack);
     EXPECT_EQ(0u, map->size());
 }
 
 
 } // WebCore namespace