Issue 4300. Support for 'external' keyword

compiler/java/com/google/dart/compiler/parser/ParserErrorCode.java

Index: compiler/java/com/google/dart/compiler/parser/ParserErrorCode.java
diff --git a/compiler/java/com/google/dart/compiler/parser/ParserErrorCode.java b/compiler/java/com/google/dart/compiler/parser/ParserErrorCode.java
index c82f74a0eb1adba7f46c94ddc82f2e932498363b..50d2edd5eb3946c12de7fcc5e0a42524b00f9c40 100644
--- a/compiler/java/com/google/dart/compiler/parser/ParserErrorCode.java
+++ b/compiler/java/com/google/dart/compiler/parser/ParserErrorCode.java
@@ -64,6 +64,9 @@ public enum ParserErrorCode implements ErrorCode {
   EXPECTED_TOKEN("Unexpected token '%s' (expected '%s')"),
   // TODO(zundel): error message needs JUnit test
   EXPECTED_VAR_FINAL_OR_TYPE("Expected 'var', 'final' or type"),
+  EXTERNAL_ONLY_METHOD("Only a top-level function, a method, a getter, a setter or an non-redirecting constructor can be specified as external"),
+  EXTERNAL_METHOD_BODY("External methods cannot have body"),
+  EXTERNAL_ABSTRACT("External methods cannot be abstract"),
   // TODO(zundel): this error message is out of date
   NATIVE_ONLY_CLASS("Native keyword can be specified only for classes"),
   NATIVE_ONLY_CORE_LIB("Native keyword can be used only in corelib"),