Implement generalized function types.

pkg/front_end/messages.yaml

 # Copyright (c) 2017, the Dart project authors.  Please see the AUTHORS file
 # for details. All rights reserved. Use of this source code is governed by a
 # BSD-style license that can be found in the LICENSE file.
 
 # Each entry in this map corresponds to a diagnostic message. Ideally, each
 # entry contains three parts:
 #
 # 1. A message template (template).
 #
 # 2. A suggestion for how to correct the problem (tip).
@@ skipping 151 matching lines @@
     - "var static foo; main(){}"
     - "var external foo; main(){}"
     - "get var foo; main(){}"
     - "set var foo; main(){}"
     - "final var foo; main(){}"
     - "var var foo; main(){}"
     - "const var foo; main(){}"
     - "abstract var foo; main(){}"
     - "static var foo; main(){}"
     - "external var foo; main(){}"
-
-ExtraneousModifierReplace:
-  template: "Can't have modifier '#lexeme' here."
-  tip: "Try replacing modifier '#lexeme' with 'var', 'final', or a type."
-  dart2jsCode: EXTRANEOUS_MODIFIER_REPLACE
-  script:
     - "set foo; main(){}"
     - "abstract foo; main(){}"
     - "static foo; main(){}"
     - "external foo; main(){}"
 
 InvalidAwaitFor:
   template: "'await' is only supported in methods with an 'async' or 'async*' body modifier."
   tip: "Try adding 'async' or 'async*' to the method body or removing the 'await' keyword."
   dart2jsCode: INVALID_AWAIT_FOR
   script: >
@@ skipping 159 matching lines @@
 AwaitAsIdentifier:
   template: "'await' can't be used as an identifier in 'async', 'async*', or 'sync*' methods."
   dart2jsCode: FASTA_IGNORED
 
 AwaitNotAsync:
   template: "'await' can only be used in 'async' or 'async*' methods."
   dart2jsCode: FASTA_IGNORED
 
 BuiltInIdentifierAsType:
   template: "Can't use '#lexeme' as a type."
-  dart2jsCode: GENERIC
+  dart2jsCode: EXTRANEOUS_MODIFIER
 
 BuiltInIdentifierInDeclaration:
   template: "Can't use '#lexeme' as a name here."
   dart2jsCode: GENERIC
 
 AwaitForNotAsync:
   template: "Asynchronous for-loop can only be used in 'async' or 'async*' methods."
   dart2jsCode: FASTA_IGNORED
 
 FactoryNotSync:
@@ skipping 20 matching lines @@
 
 YieldNotGenerator:
   template: "'yield' can only be used in 'sync*' or 'async*' methods."
   dart2jsCode: FASTA_IGNORED
 
 OnlyTry:
   template: "Try block should be followed by 'on', 'catch', or 'finally' block."
   tip: "Did you forget to add a 'finally' block?"
   statement: "try {}"
   dart2jsCode: FASTA_IGNORED
+
+TypeAfterVar:
+  template: "Can't have both a type and 'var'."
+  tip: "Try removing 'var.'"
+  dart2jsCode: EXTRANEOUS_MODIFIER
+
+TypeRequired:
+  template: "A type or modifier is required here."
+  tip: "Try adding a type, 'var', 'const', or 'final'."