Fix AIX compiler warning

Fix AIX compiler warning indicating that variable may not be
initialized

	modified:   src/heap/heap.cc

R=danno@chromium.org, svenpanne@chromium.org, mbrandy@us.ibm.com

BUG=

Review URL: https://codereview.chromium.org/1112883002

Cr-Commit-Position: refs/heads/master@{#28145}

src/heap/heap.cc

@@ -3724,7 +3724,7 @@ AllocationResult Heap::CopyCode(Code* code) {
     new_constant_pool = empty_constant_pool_array();
   }
 
-  HeapObject* result;
+  HeapObject* result = NULL;
   // Allocate an object the same size as the code object.
   int obj_size = code->Size();
   allocation = AllocateRaw(obj_size, CODE_SPACE, CODE_SPACE);