Fixed DoMulI to adopt correct operand size when the representation is Smi

src/runtime.cc

Index: src/runtime.cc
diff --git a/src/runtime.cc b/src/runtime.cc
index a9121ce851d578c650e45d2083bbbdd857bcb489..27ab6ec0d22847e2af8514f9aa67d06aaa52b639 100644
--- a/src/runtime.cc
+++ b/src/runtime.cc
@@ -4688,6 +4688,19 @@ RUNTIME_FUNCTION(MaybeObject*, Runtime_NumberToPrecision) {
 }
 
 
+RUNTIME_FUNCTION(MaybeObject*, Runtime_IsValidSmi) {
+  HandleScope shs(isolate);
+  ASSERT(args.length() == 1);
+
+  CONVERT_NUMBER_CHECKED(int32_t, number, Int32, args[0]);
+  if (Smi::IsValid(number)) {
+    return isolate->heap()->true_value();
+  } else {
+    return isolate->heap()->false_value();
+  }
+}
+
+
 // Returns a single character string where first character equals
 // string->Get(index).
 static Handle<Object> GetCharAt(Handle<String> string, uint32_t index) {