Implement messages in assert() in dev_compiler.

pkg/dev_compiler/tool/input_sdk/private/ddc_runtime/operations.dart

Index: pkg/dev_compiler/tool/input_sdk/private/ddc_runtime/operations.dart
diff --git a/pkg/dev_compiler/tool/input_sdk/private/ddc_runtime/operations.dart b/pkg/dev_compiler/tool/input_sdk/private/ddc_runtime/operations.dart
index 0e3acaf539e93fd4692da3833e2ab2b24491be9b..a3c80f0527d3ba85e80095d7b25a3ef7cec48911 100644
--- a/pkg/dev_compiler/tool/input_sdk/private/ddc_runtime/operations.dart
+++ b/pkg/dev_compiler/tool/input_sdk/private/ddc_runtime/operations.dart
@@ -312,7 +312,8 @@ dsend(obj, method, @rest args) => _callMethod(obj, method, null, args, method);
 dgsend(obj, typeArgs, method, @rest args) =>
     _callMethod(obj, method, typeArgs, args, method);
 
-dindex(obj, index) => _callMethod(obj, '_get', null, JS('', '[#]', index), '[]');
+dindex(obj, index) =>
+    _callMethod(obj, '_get', null, JS('', '[#]', index), '[]');
 
 dsetindex(obj, index, value) =>
     _callMethod(obj, '_set', null, JS('', '[#, #]', index, value), '[]=');
@@ -552,6 +553,13 @@ assert_(condition) => JS(
   if (!$condition) $throwAssertionError();

[Jennifer Messerly, 2016/12/12 22:36:02]

here's how I would change this:

assert_(condition, [message]) => JS( // ...

if (!$condition) $throwAssertionError($message);

[Bob Nystrom, 2016/12/13 19:29:51]

Done.

 })()''');
 
+@JSExportName('assertMessage')
+assertMessage_(condition, message) => JS(

[Jennifer Messerly, 2016/12/12 22:36:02]

this can be removed per earlier suggestions

[Bob Nystrom, 2016/12/13 19:29:51]

Done.

+    '',
+    '''(() => {
+  if (!$condition) $throwAssertionErrorWithMessage(message());
+})()''');
+
 var _stack = null;
 @JSExportName('throw')
 throw_(obj) => JS(