Add guard against self assignment.

BUG=
TEST=

Review URL: https://chromiumcodereview.appspot.com/10537024

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@11756 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

src/hydrogen.cc

@@ -1364,7 +1364,9 @@ HSideEffectMap::HSideEffectMap(HSideEffectMap* other) : count_(other->count_) {
 
 
 HSideEffectMap& HSideEffectMap::operator= (const HSideEffectMap& other) {
-  memcpy(data_, other.data_, kNumberOfTrackedSideEffects * kPointerSize);
+  if (this != &other) {
+    memcpy(data_, other.data_, kNumberOfTrackedSideEffects * kPointerSize);
+  }
   return *this;
 }