Issue 5929. Ignore 'patch' before 'class'.

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

Index: compiler/java/com/google/dart/compiler/parser/DartParser.java
diff --git a/compiler/java/com/google/dart/compiler/parser/DartParser.java b/compiler/java/com/google/dart/compiler/parser/DartParser.java
index 1880f3c35f8eb04df22da80766ce5735da45f7f6..e3d786119dee00fd6452dd9b64b91ae508b9cc08 100644
--- a/compiler/java/com/google/dart/compiler/parser/DartParser.java
+++ b/compiler/java/com/google/dart/compiler/parser/DartParser.java
@@ -167,6 +167,8 @@ public class DartParser extends CompletionHooksParserBase {
   private static final String SHOW_KEYWORD = "show";
   private static final String STATIC_KEYWORD = "static";
   private static final String TYPEDEF_KEYWORD = "typedef";
+  // does not exist in specification
+  private static final String PATCH_KEYWORD = "patch";
 
 
   public static final String[] PSEUDO_KEYWORDS = {
@@ -324,6 +326,9 @@ public class DartParser extends CompletionHooksParserBase {
           isTopLevelAbstract = true;
           topLevelAbstractModifierPosition = position();
         }
+        // skip "patch" before "class"
+        if (peek(1) == Token.CLASS && optionalPseudoKeyword(PATCH_KEYWORD)) {
+        }
         // Parse top level element.
         if (optional(Token.CLASS)) {
           isParsingClass = true;