Use static dispatch for dynamic on Object methods

lib/src/compiler/code_generator.dart

Index: lib/src/compiler/code_generator.dart
diff --git a/lib/src/compiler/code_generator.dart b/lib/src/compiler/code_generator.dart
index 43de895f24bd03427106230beb2078f5d600b6e6..77820f188a561cbeefa8563f4c21a9e66c185cf9 100644
--- a/lib/src/compiler/code_generator.dart
+++ b/lib/src/compiler/code_generator.dart
@@ -3130,7 +3130,7 @@ class CodeGenerator extends GeneralizingAstVisitor
   }
 
   bool _requiresStaticDispatch(Expression target, String memberName) {
-    var type = getStaticType(target);
+    var type = target.propagatedType ?? getStaticType(target);

[Harry Terkelsen, 2016/04/26 20:51:55]

btw, this is the only use of propagatedType in ddc... I wasn't sure if the
analyzer API changed and getStaticType should give propagatedType if it is set
or if there was a reason not to use it?

[Jennifer Messerly, 2016/04/26 21:04:56]

yeah we never to use it. It's the old Analyzer inference, it's unsound and it's
also something we hope to remove from Strong Mode Analyzer in the near future
(we waste time in some cases inferring things twice, the old way and the new
way).

... so I don't think this is the right fix, but it's a great find :). So what
this means is old-Analyzer inferred something different than new-Strong-Mode
did. We should have a look into the example and the Analyzer code and figure out
why this happened & fix it over there.

This is the function that's supposed to be inferring the correct type for us:
https://github.com/dart-lang/sdk/blob/2bd7317edee49e5365e593e22dee52d95ed7356...

Maybe the logic got broken somehow, but it used to work.

     if (!isObjectProperty(memberName)) {
       return false;
     }