Issue 5292. Unreferenced imported identifiers should not be an error

compiler/java/com/google/dart/compiler/resolver/ResolverErrorCode.java

Index: compiler/java/com/google/dart/compiler/resolver/ResolverErrorCode.java
diff --git a/compiler/java/com/google/dart/compiler/resolver/ResolverErrorCode.java b/compiler/java/com/google/dart/compiler/resolver/ResolverErrorCode.java
index f0fa87eb52d36d51fcb2ba4506a3f49433247f35..534aa867b90c39b442c86d0c90473af0da4bff8e 100644
--- a/compiler/java/com/google/dart/compiler/resolver/ResolverErrorCode.java
+++ b/compiler/java/com/google/dart/compiler/resolver/ResolverErrorCode.java
@@ -84,6 +84,8 @@ public enum ResolverErrorCode implements ErrorCode {
       "Deprecated Map literal syntax. Both String (as key) and value type arguments required."),
   DID_YOU_MEAN_NEW("%1$s is a %2$s. Did you mean (new %1$s)?"),
   DUPLICATE_IMPLEMENTS_TYPE("Duplicate type in the implements clause"),
+  DUPLICATE_IMPORTED_NAME("Element '%s' is introduced by %s imports: %s"),
+  DUPLICATE_IMPORTED_NAME_TYPE(ErrorSeverity.WARNING, "Element '%s' is introduced by %s imports: %s"),
   DUPLICATE_INITIALIZATION("Duplicate initialization of '%s'"),
   DUPLICATE_FUNCTION_EXPRESSION("Duplicate function expression '%s'"),
   DUPLICATE_LABEL_IN_SWITCH_STATEMENT("Duplicate label in switch statement"),
@@ -92,7 +94,6 @@ public enum ResolverErrorCode implements ErrorCode {
   DUPLICATE_NAMED_ARGUMENT("Duplicate named parameter argument"),
   DUPLICATE_PARAMETER("Duplicate parameter '%s'"),
   DUPLICATE_TOP_LEVEL_DECLARATION("duplicate top-level declaration %s at %s"),
-  DUPLICATE_TOP_LEVEL_DECLARATION_IMPORT("Duplicate import '%s' in %s prefix '%s' -  %s - %s"),
   DUPLICATE_TYPE_VARIABLE("Duplicate type variable '%s'"),
   // TODO(zundel): error message needs JUnit test, (reachable code?)
   EXPECTED_AN_INSTANCE_FIELD_IN_SUPER_CLASS(