Speed up identifying keywords in scanner, by using extra table.

runtime/vm/scanner.h

 // Copyright (c) 2011, 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.
 //
 // Scanner class for the Dart language. The scanner reads source text
 // and produces a stream of tokens which is used by the parser.
 //
 
 #ifndef VM_SCANNER_H_
 #define VM_SCANNER_H_
@@ skipping 67 matching lines @@
   static bool IsIdent(const String& str);
 
   // Does the token stream contain a valid literal. This is used to implement
   // the Dart methods int.parse and double.parse.
   static bool IsValidLiteral(const Scanner::GrowableTokenStream& tokens,
                              Token::Kind literal_kind,
                              bool* is_positive,
                              const String** value);
 
  private:
+  static const int kNumLowercaseChars = 26;
+
   struct ScanContext {
     ScanContext* next;
     char string_delimiter;
     bool string_is_multiline;
     int  brace_level;
   };
 
   struct KeywordTable {
     Token::Kind kind;
     const char* keyword_chars;
@@ skipping 100 matching lines @@
   // and its interpolated expressions.
   ScanContext* saved_context_;
   int32_t string_delimiter_;
   bool string_is_multiline_;
   int brace_level_;
 
   const String& private_key_;
 
   SourcePosition c0_pos_;      // Source position of lookahead character c0_.
 
-  static KeywordTable keywords_[Token::numKeywords];
+  static KeywordTable keywords_[Token::kNumKeywords];
+  static int keywords_char_offset_[kNumLowercaseChars];
 };
 
 
 }  // namespace dart
 
 #endif  // VM_SCANNER_H_