Update semantic highlighting only if there are no parse errors

compiler/javatests/com/google/dart/compiler/parser/SyntaxTest.java

Index: compiler/javatests/com/google/dart/compiler/parser/SyntaxTest.java
diff --git a/compiler/javatests/com/google/dart/compiler/parser/SyntaxTest.java b/compiler/javatests/com/google/dart/compiler/parser/SyntaxTest.java
index 7bf53403aaa6d3d2f2cca61d0ff24333ce074e68..f977713fa14adbe3192780cfc40dc772f893b206 100644
--- a/compiler/javatests/com/google/dart/compiler/parser/SyntaxTest.java
+++ b/compiler/javatests/com/google/dart/compiler/parser/SyntaxTest.java
@@ -55,6 +55,16 @@ public class SyntaxTest extends AbstractParserTest {
         "export 'a.dart';"));
   }
 
+  public void test_hasParseErrors_true() {
+    DartUnit unit = parseSource("garbage").getDartUnit();
+    assertTrue(unit.hasParseErrors());
+  }
+  
+  public void test_hasParseErrors_false() {
+    DartUnit unit = parseSource("// empty").getDartUnit();
+    assertFalse(unit.hasParseErrors());
+  }
+  
   public void test_importDirective_noUri() {
     DartUnit unit = parseUnit("test.dart", Joiner.on("\n").join(
         "library lib;",