Add %LoadMutableDouble index check.

src/field-index-inl.h

Index: src/field-index-inl.h
diff --git a/src/field-index-inl.h b/src/field-index-inl.h
index 198422feef4b65f21c7f5c14cc867cc306fb1ff9..80e486945b48eecb7944b3be34b04256a167112b 100644
--- a/src/field-index-inl.h
+++ b/src/field-index-inl.h
@@ -69,6 +69,18 @@ inline FieldIndex FieldIndex::ForLoadByFieldIndex(Map* map, int orig_index) {
 }
 
 
+inline bool FieldIndex::LoadByFieldIndexValid(int index) {
+  index >>= 1;
+  if (index < 0) {
+    index = -(index + 1);
+    index += FixedArray::kHeaderSize / kPointerSize;
+  } else {
+    index += JSObject::kHeaderSize / kPointerSize;
+  }
+  return IndexBits::is_valid(index);
+}
+
+
 // Returns the index format accepted by the HLoadFieldByIndex instruction.
 // (In-object: zero-based from (object start + JSObject::kHeaderSize),
 // out-of-object: zero-based from FixedArray::kHeaderSize.)