Don't output tons of messages on apidoc.

sdk/lib/_internal/compiler/implementation/library_loader.dart

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 part of dart2js;
 
 /**
  * [CompilerTask] for loading libraries and setting up the import/export scopes.
  *
  * The library loader uses four different kinds of URIs in different parts of
@@ skipping 302 matching lines @@
     LibraryName tag = library.libraryTag;
     if (tag != null) {
       String name = library.getLibraryOrScriptName();
       LibraryElement existing =
           libraryNames.putIfAbsent(name, () => library);
       if (!identical(existing, library)) {
         Uri uri = library.entryCompilationUnit.script.uri;
         compiler.reportMessage(
             compiler.spanFromSpannable(tag.name, uri),
             MessageKind.DUPLICATED_LIBRARY_NAME.error({'libraryName': name}),
-            api.Diagnostic.WARNING);
+            api.Diagnostic.VERBOSE_INFO);
         Uri existingUri = existing.entryCompilationUnit.script.uri;
         compiler.reportMessage(
             compiler.spanFromSpannable(existing.libraryTag.name, existingUri),
             MessageKind.DUPLICATED_LIBRARY_NAME.error({'libraryName': name}),
-            api.Diagnostic.WARNING);
+            api.Diagnostic.VERBOSE_INFO);
       }
     }
   }
 
   bool isDartCore(Uri uri) => uri.scheme == "dart" && uri.path == "core";
 
   /**
    * Lazily loads and returns the [LibraryElement] for the dart:core library.
    */
   LibraryElement loadCoreLibrary(LibraryDependencyHandler handler) {
@@ skipping 492 matching lines @@
   }
 
   /**
    * Registers all top-level entities of [library] as starting point for the
    * fixed-point computation of the import/export scopes.
    */
   void registerLibraryExports(LibraryElement library) {
     nodeMap[library].registerInitialExports();
   }
 }