Oilpan: Support polymorphic objects in HeapVectorBackings

Source/wtf/Vector.h

Index: Source/wtf/Vector.h
diff --git a/Source/wtf/Vector.h b/Source/wtf/Vector.h
index 6a52675cb750dba0308bb88990634058930791e2..35f47926eb226c63afb6e9e1a33cd7d1b9030b1b 100644
--- a/Source/wtf/Vector.h
+++ b/Source/wtf/Vector.h
@@ -90,7 +90,9 @@ static const size_t kInitialVectorSize = WTF_VECTOR_INITIAL_SIZE;
     struct VectorUnusedSlotClearer<true, T> {
         static void clear(T* begin, T* end)
         {
-            memset(begin, 0, sizeof(T) * (end - begin));
+            char* array = reinterpret_cast<char*>(begin);
+            for (size_t i = 0; i < sizeof(T) * (end - begin); i++)
+                array[i] = 0;

[haraken, 2015/04/27 06:57:57]

We cannot now use memset here because clang complains that we should not use
memset for slots that contain vtables. Yeah, but we do want to do that here :)

[sof, 2015/04/30 21:15:47]

It might rewrite that loop to a memset() application internally -- I seem to
remember some amusing breakage we had in the past which ran into this (kouhei
fixed it, iirc.)

Wouldn't it work to do memset(reinterpret_cast<void*>(begin), ...) ? 

[haraken, 2015/04/30 23:40:20]

Thanks, it works.

         }
 
 #if ENABLE(ASSERT)