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

runtime/vm/symbols.cc

Index: runtime/vm/symbols.cc
diff --git a/runtime/vm/symbols.cc b/runtime/vm/symbols.cc
index 754de7e2dd1a28fd9043e1143cc71d4d827bc5ae..5f1d8d00b9155a32030e029310110e286590363b 100644
--- a/runtime/vm/symbols.cc
+++ b/runtime/vm/symbols.cc
@@ -49,7 +49,7 @@ const char* Symbols::Name(SymbolId symbol) {
 
 const String& Symbols::Keyword(Token::Kind keyword) {
   const int kw_index = keyword - Token::kFirstKeyword;
-  ASSERT((0 <= kw_index) && (kw_index < Token::numKeywords));
+  ASSERT((0 <= kw_index) && (kw_index < Token::kNumKeywords));
   // First keyword symbol is in symbol_handles_[kKwTableStart + 1].
   const intptr_t keyword_id = Symbols::kKwTableStart + 1 + kw_index;
   ASSERT(symbol_handles_[keyword_id] != NULL);