Fix build on arm/x64 after r17840.

TBR=jkummerow@chromium.org
BUG=v8:3013
LOG=N

Review URL: https://codereview.chromium.org/75353002

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@17843 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

src/v8conversions.h

@@ -84,7 +84,7 @@ inline bool TryNumberToSize(Isolate* isolate,
 // Converts a number into size_t.
 inline size_t NumberToSize(Isolate* isolate,
                            Object* number) {
-  size_t result;
+  size_t result = 0;
   bool is_valid = TryNumberToSize(isolate, number, &result);
   CHECK(is_valid);
   return result;