Add `=` as default-value separator for named parameters.

runtime/vm/parser.cc

 // Copyright (c) 2012, 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.
 
 #include "vm/parser.h"
 #include "vm/flags.h"
 
 #ifndef DART_PRECOMPILED_RUNTIME
 
 #include "lib/invocation_mirror.h"
@@ skipping 2166 matching lines @@
 
   if ((CurrentToken() == Token::kASSIGN) || (CurrentToken() == Token::kCOLON)) {
     if ((!params->has_optional_positional_parameters &&
          !params->has_optional_named_parameters) ||
         !allow_explicit_default_value) {
       ReportError("parameter must not specify a default value");
     }
     if (params->has_optional_positional_parameters) {
       ExpectToken(Token::kASSIGN);
     } else {
-      ExpectToken(Token::kCOLON);
+      ConsumeToken();

[eernst, 2016/10/11 20:59:50]

It was not obvious to me why this would work, but here's the reason I found: (1)
ConsumeToken() consumes the same token which is tested in line 2178, and (2)
ReportError cannot return. Then we know that the consumed token is '=' or ':',
and that `params->has_optional_named_parameters` is true.

[Lasse Reichstein Nielsen, 2016/10/12 06:10:58]

Correct.
ConsumeToken is used to drop the current token and advance to the next, no
matter what it is. It's only used when we have already tested the current token
somewhere else and know what it is.
The ReportError does unwind the stack to report the error. You could think that
it throws (I actually think it longjumps, but potato-potatoh).

     }
     params->num_optional_parameters++;
     params->has_explicit_default_values = true;  // Also if explicitly NULL.
     if (is_top_level_) {
       // Skip default value parsing.
       SkipExpr();
     } else {
       const Instance& const_value = ParseConstExpr()->literal();
       parameter.default_value = &const_value;
     }
@@ skipping 12896 matching lines @@
     const ArgumentListNode& function_args,
     const LocalVariable* temp_for_last_arg,
     bool is_super_invocation) {
   UNREACHABLE();
   return NULL;
 }
 
 }  // namespace dart
 
 #endif  // DART_PRECOMPILED_RUNTIME