dart2js: add --preserve-uris flag.

sdk/lib/_internal/compiler/implementation/js_backend/backend.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 js_backend;
 
 const VERBOSE_OPTIMIZER_HINTS = false;
 
 class JavaScriptItemCompilationContext extends ItemCompilationContext {
   final Set<HInstruction> boundsChecked = new Set<HInstruction>();
@@ skipping 1538 matching lines @@
   void registerStaticUse(Element element, Enqueuer enqueuer) {
     if (element == disableTreeShakingMarker) {
       compiler.disableTypeInferenceForMirrors = true;
       isTreeShakingDisabled = true;
       typeVariableHandler.onTreeShakingDisabled(enqueuer);
     } else if (element == preserveNamesMarker) {
       mustPreserveNames = true;
     } else if (element == preserveMetadataMarker) {
       mustRetainMetadata = true;
     } else if (element == preserveUrisMarker) {
-      mustRetainUris = true;
+      if (!compiler.hideUris) mustRetainUris = true;
     } else if (element == preserveLibraryNamesMarker) {
       mustRetainLibraryNames = true;
     } else if (element == getIsolateAffinityTagMarker) {
       needToInitializeIsolateAffinityTag = true;
     } else if (element.isDeferredLoaderGetter) {
       // TODO(sigurdm): Create a function registerLoadLibraryAccess.
       if (compiler.loadLibraryFunction == null) {
         compiler.loadLibraryFunction =
             findHelper("_loadLibraryWrapper");
         enqueueInResolution(compiler.loadLibraryFunction,
@@ skipping 837 matching lines @@
   }
 }
 
 /// Records that [constant] is used by the element behind [registry].
 class Dependency {
   final Constant constant;
   final Element annotatedElement;
 
   const Dependency(this.constant, this.annotatedElement);
 }