Use new ASAN APIs for scanning ASAN fake stacks during garbage collection.

Source/heap/ThreadState.h

Index: Source/heap/ThreadState.h
diff --git a/Source/heap/ThreadState.h b/Source/heap/ThreadState.h
index 6348585696056e2326f468b4dc40b1f6bd99c405..d8ead1d7b0c4d70f7051ee522ab3c45c62d3187b 100644
--- a/Source/heap/ThreadState.h
+++ b/Source/heap/ThreadState.h
@@ -426,6 +426,12 @@ public:
     // Visit local thread stack and trace all pointers conservatively.
     void visitStack(Visitor*);
 
+#if defined(ADDRESS_SANITIZER) && !OS(WIN)
+    // Visit the asan fake stack frame corresponding to a slot on the
+    // real machine stack if there is one.
+    void visitAsanFakeStackForPointer(Visitor*, Address);
+#endif
+
     // Visit all persistents allocated on this thread.
     void visitPersistents(Visitor*);
 
@@ -487,6 +493,9 @@ private:
     HeapContainsCache* m_heapContainsCache;
     HeapStats m_stats;
     HeapStats m_statsAfterLastGC;
+#if defined(ADDRESS_SANITIZER) && !OS(WIN)

[kcc1, 2014/02/06 13:44:06]

Why !OS(WIN)?
asan will be available on Windows eventually

[Mads Ager (chromium), 2014/02/06 14:15:17]

SyZyAsan uses the same define and they do not have this API (and they don't have
a fake stack). So, we shouldn't attempt to do this on Windows. 

+    void* m_asanFakeStack;
+#endif
 };
 
 template<ThreadAffinity affinity> class ThreadStateFor;