Add missing javascript integer overflow check on 64-bit platforms.

runtime/vm/object.cc

Index: runtime/vm/object.cc
===================================================================
--- runtime/vm/object.cc	(revision 37239)
+++ runtime/vm/object.cc	(working copy)
@@ -15130,15 +15130,17 @@
 
 
 RawInteger* Integer::New(int64_t value, Heap::Space space, const bool silent) {
-  if ((value <= Smi::kMaxValue) && (value >= Smi::kMinValue)) {
-    return Smi::New(value);
-  }
+  const bool is_smi = (value <= Smi::kMaxValue) && (value >= Smi::kMinValue);
   if (!silent &&
       FLAG_throw_on_javascript_int_overflow &&
       !IsJavascriptInt(value)) {
-    const Integer& i = Integer::Handle(Mint::New(value));
+    const Integer& i = is_smi ? Integer::Handle(Smi::New(value))
+                              : Integer::Handle(Mint::New(value));
     ThrowJavascriptIntegerOverflow(i);
   }
+  if (is_smi) {
+    return Smi::New(value);
+  }
   return Mint::New(value, space);
 }