Report CONST_MAP_KEY_EXPRESSION_TYPE_IMPLEMENTS_EQUALS.

editor/tools/plugins/com.google.dart.engine/src/com/google/dart/engine/error/CompileTimeErrorCode.java

Index: editor/tools/plugins/com.google.dart.engine/src/com/google/dart/engine/error/CompileTimeErrorCode.java
diff --git a/editor/tools/plugins/com.google.dart.engine/src/com/google/dart/engine/error/CompileTimeErrorCode.java b/editor/tools/plugins/com.google.dart.engine/src/com/google/dart/engine/error/CompileTimeErrorCode.java
index 7f0f1ceafcea0128181f99195603b18b79e96361..2c99c6a6acbca36b186df3f0014f8484c2249b67 100644
--- a/editor/tools/plugins/com.google.dart.engine/src/com/google/dart/engine/error/CompileTimeErrorCode.java
+++ b/editor/tools/plugins/com.google.dart.engine/src/com/google/dart/engine/error/CompileTimeErrorCode.java
@@ -171,6 +171,14 @@ public enum CompileTimeErrorCode implements ErrorCode {
   CONST_INSTANCE_FIELD("Only static fields can be declared as 'const'"),
 
   /**
+   * 12.8 Maps: It is a compile-time error if the key of an entry in a constant map literal is an
+   * instance of a class that implements the operator <i>==</i> unless the key is a string or
+   * integer.
+   */
+  CONST_MAP_KEY_EXPRESSION_TYPE_IMPLEMENTS_EQUALS(
+      "The constant map entry key expression type '%s' cannot override the == operator"),
+
+  /**
    * 5 Variables: A constant variable must be initialized to a compile-time constant (12.1) or a
    * compile-time error occurs.
    *