Issue 1475. Report warning for non-unique Map literal keys.

compiler/javatests/com/google/dart/compiler/type/TypeAnalyzerCompilerTest.java

Index: compiler/javatests/com/google/dart/compiler/type/TypeAnalyzerCompilerTest.java
diff --git a/compiler/javatests/com/google/dart/compiler/type/TypeAnalyzerCompilerTest.java b/compiler/javatests/com/google/dart/compiler/type/TypeAnalyzerCompilerTest.java
index ce35c48c953e2fe1948bb5e7d1d6380174de5edb..6fc6188ba65564214c666af0727dfa500e61a99a 100644
--- a/compiler/javatests/com/google/dart/compiler/type/TypeAnalyzerCompilerTest.java
+++ b/compiler/javatests/com/google/dart/compiler/type/TypeAnalyzerCompilerTest.java
@@ -828,4 +828,13 @@ public class TypeAnalyzerCompilerTest extends CompilerTestCase {
         });
     return errors;
   }
+
+  public void test_mapLiteralKeysUnique() throws Exception {
+    List<DartCompilationError> errors =
+        analyzeLibrarySourceErrors(makeCode(
+            "// filler filler filler filler filler filler filler filler filler filler",
+            "var m = {'a' : 0, 'b': 1, 'a': 2};",
+            ""));
+    assertErrors(errors, errEx(TypeErrorCode.MAP_LITERAL_KEY_UNIQUE, 2, 27, 3));
+  }
 }