Retain elements a finer granularity than library.

dart/sdk/lib/_internal/compiler/compiler.dart

Index: dart/sdk/lib/_internal/compiler/compiler.dart
diff --git a/dart/sdk/lib/_internal/compiler/compiler.dart b/dart/sdk/lib/_internal/compiler/compiler.dart
index 8e5f77f77844433e3f2eddaadd0ddba2db095250..abeb36c459404f519ed5149807260d41ed4d8db8 100644
--- a/dart/sdk/lib/_internal/compiler/compiler.dart
+++ b/dart/sdk/lib/_internal/compiler/compiler.dart
@@ -140,7 +140,12 @@ class Diagnostic {
   static const Diagnostic HINT = const Diagnostic(4, 'hint');
 
   /**
-   * Informational messages.
+   * Additional information about the preceding non-info diagnostic from the
+   * compiler.
+   *
+   * For example, consider a duplicated definition. The compiler first emits a
+   * message about the duplicated definition, then emits an info message about
+   * the location of the existing definition.
    */
   static const Diagnostic INFO = const Diagnostic(8, 'info');