Address comment from vm-based keyword symbols CL

runtime/vm/symbols.cc

Index: runtime/vm/symbols.cc
===================================================================
--- runtime/vm/symbols.cc	(revision 30289)
+++ runtime/vm/symbols.cc	(working copy)
@@ -50,8 +50,8 @@
 const String& Symbols::Keyword(Token::Kind keyword) {
   const int kw_index = keyword - Token::kFirstKeyword;
   ASSERT((0 <= kw_index) && (kw_index < Token::numKeywords));
-  ASSERT(Token::kABSTRACT == Token::kFirstKeyword);
-  const intptr_t keyword_id = Symbols::kABSTRACTId + kw_index;
+  // 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);
   return *symbol_handles_[keyword_id];
 }