This patch disentangles dart:jni from //sky/engine and moves it into
//flutter/lib/jni. Eventually dart:ui will move into a peer directory.

Add more rules to determine which overloaded Java method should be invoked
for a given Dart call.  In particular, check whether the class of a
Dart-wrapped Java object matches the type declared for the corresponding
argument in the Java method.

Example:
  JavaClass dateFormatClass = Java.getClass('java.text.SimpleDateFormat');
  JavaObject format = dateFormatClass.newInstance('yyyy.MM.dd');
  print(format.parse('2016.01.01').getYear());