Convert serialized values to ints if they are whole and less than 53 bits.

Source/bindings/dart/V8Converter.cpp

Index: Source/bindings/dart/V8Converter.cpp
diff --git a/Source/bindings/dart/V8Converter.cpp b/Source/bindings/dart/V8Converter.cpp
index dd399ffb241fbd9f611929765f23af4a9e0154d6..ed4f4061001498c79e53507eb3623b901a39e1f2 100644
--- a/Source/bindings/dart/V8Converter.cpp
+++ b/Source/bindings/dart/V8Converter.cpp
@@ -170,8 +170,10 @@ Dart_Handle V8Converter::toDart(v8::Handle<v8::Value> value, V8ToDartMap& map, D
         return Dart_Null();
     if (value->IsString())
         return map.put(value, stringToDart(value));
-    if (value->IsInt32())
-        return Dart_NewInteger(value->Int32Value());
+    if (value->IsNumber() && abs(value->IntegerValue()) <= pow(2, 53)) {
+        // JS can store integer values that are no greater than 2^53.
+        return Dart_NewInteger(value->IntegerValue());
+    }
     if (value->IsBoolean())
         return Dart_NewBoolean(value->BooleanValue());
     if (value->IsNumber())