Update the mojom lexer to emit comment tokens.

mojom/mojom_parser/lexer/tokens.go

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 //
 // TokenKinds is a type which describes the kinds of tokens which can be
 // encountered in a mojom file.
 
 package lexer
 
 import (
@@ skipping 49 matching lines @@
         True
         False
         Default
 
         // Constants
         IntConstDec
         IntConstHex
         FloatConst
         Ordinal
         StringLiteral
+
+        // Comments
+        SingleLineComment
+        MultiLineComment
 )
 
 // This method is used to generate user-facing strings in compilation error
 // messages. For example for LBrace we produce the string "'{'". Notice the
 // single-quotes. This will be used for example in an error message that looks
 // like the following:
 // Unexpected token at line 5, column 6: '###'. Expecting '{'.
 func (tokenKind TokenKind) String() string {
         switch tokenKind {
         // Errors
@@ skipping 209 matching lines @@
                 snippetBuffer.WriteString("\x1b[32;1m")
         }
         snippetBuffer.WriteString(strings.Repeat("^", tokenSize))
         if color {
                 // Reset all printing attributes.
                 snippetBuffer.WriteString("\x1b[0m")
         }
         snippet = snippetBuffer.String()
         return
 }