dart2js: add --preserve-uris flag.

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

Index: sdk/lib/_internal/compiler/implementation/compiler.dart
diff --git a/sdk/lib/_internal/compiler/implementation/compiler.dart b/sdk/lib/_internal/compiler/implementation/compiler.dart
index c278a58c92f8a91eedb69cb29c6abbe5362c9f85..fbc76ebec13c4f296f20844ebf88c0bf783834e3 100644
--- a/sdk/lib/_internal/compiler/implementation/compiler.dart
+++ b/sdk/lib/_internal/compiler/implementation/compiler.dart
@@ -641,6 +641,10 @@ abstract class Compiler implements DiagnosticListener {
       new ResolutionRegistry.internal(null, new TreeElementMapping(null));
 
   final bool enableMinification;
+
+  /// When `true` doesn't emit URIs in the reflection metadata.
+  final bool hideUris;
+
   final bool enableTypeAssertions;
   final bool enableUserAssertions;
   final bool trustTypeAnnotations;
@@ -930,6 +934,7 @@ abstract class Compiler implements DiagnosticListener {
             bool disableTypeInferenceFlag: false,
             this.maxConcreteTypeSize: 5,
             this.enableMinification: false,
+            this.hideUris: false,
             this.enableNativeLiveTypeAnalysis: false,
             bool emitJavaScript: true,
             bool dart2dartMultiFile: false,