Library prefix should be an identifier

vm/parser.cc

Index: vm/parser.cc
===================================================================
--- vm/parser.cc	(revision 1714)
+++ vm/parser.cc	(working copy)
@@ -3162,6 +3162,10 @@
         ErrorMsg("prefix expected");
       }
       prefix = CurrentLiteral()->raw();
+      // TODO(asiva): Need to also check that prefix is not a reserved keyword.
+      if (!Scanner::IsIdent(prefix)) {
+        ErrorMsg("prefix should be an identifier");
+      }
       ConsumeToken();
     }
     ExpectToken(Token::kRPAREN);