Issue 3532. Report error if one unit included twice

compiler/javatests/com/google/dart/compiler/end2end/inc/IncrementalCompilation2Test.java

Index: compiler/javatests/com/google/dart/compiler/end2end/inc/IncrementalCompilation2Test.java
diff --git a/compiler/javatests/com/google/dart/compiler/end2end/inc/IncrementalCompilation2Test.java b/compiler/javatests/com/google/dart/compiler/end2end/inc/IncrementalCompilation2Test.java
index a27ba5747a3d0279b8ce29898484419d07fc0a32..2bcd2bdae442e5a70e1bf3649db1a203bbd23420 100644
--- a/compiler/javatests/com/google/dart/compiler/end2end/inc/IncrementalCompilation2Test.java
+++ b/compiler/javatests/com/google/dart/compiler/end2end/inc/IncrementalCompilation2Test.java
@@ -671,6 +671,28 @@ public class IncrementalCompilation2Test extends CompilerTestCase {
     // should not cause exception
     assertFalse(source.exists());
   }
+  /**
+   * <p>
+   * http://code.google.com/p/dart/issues/detail?id=3532
+   */
+  public void test_includeSameUnitTwice() throws Exception {
+    appSource.setContent(
+        "A.dart",
+        makeCode(
+            "// filler filler filler filler filler filler filler filler filler filler filler",
+            ""));
+    appSource.setContent(
+        APP,
+        makeCode(
+            "// filler filler filler filler filler filler filler filler filler filler filler",
+            "#library('application');",
+            "#source('A.dart');",
+            "#source('A.dart');",
+            ""));
+    // do compile, no errors expected
+    compile();
+    assertErrors(errors, errEx(DartCompilerErrorCode.UNIT_WAS_ALREADY_INCLUDED, 4, 1, 18));
+  }
 
   /**
    * There was bug that we added <code>null</code> into {@link LibraryUnit#getImports()}. Here trick