Add _embedder.yaml support to analyzer and analysis_server

pkg/analysis_server/lib/src/analysis_server.dart

Index: pkg/analysis_server/lib/src/analysis_server.dart
diff --git a/pkg/analysis_server/lib/src/analysis_server.dart b/pkg/analysis_server/lib/src/analysis_server.dart
index 458cdd727cbe31e76842fc509844b9dc89ddaec2..063188e236369b3ecce6efbfdc90b30af3b2ad88 100644
--- a/pkg/analysis_server/lib/src/analysis_server.dart
+++ b/pkg/analysis_server/lib/src/analysis_server.dart
@@ -24,6 +24,7 @@ import 'package:analysis_server/src/services/index/index.dart';
 import 'package:analysis_server/src/services/search/search_engine.dart';
 import 'package:analyzer/file_system/file_system.dart';
 import 'package:analyzer/instrumentation/instrumentation.dart';
+import 'package:analyzer/source/embedder.dart';
 import 'package:analyzer/source/pub_package_map_provider.dart';
 import 'package:analyzer/src/generated/ast.dart';
 import 'package:analyzer/src/generated/element.dart';
@@ -1524,17 +1525,34 @@ class ServerContextManagerCallbacks extends ContextManagerCallbacks {
     }
   }
 
+  /// Returns true if the list of [resolvers] contains a [EmbedderUriResolver]
+  /// with at least one url mapping.
+  static bool _useEmbedderUriResolver(List<UriResolver> resolvers) {
+    for (UriResolver resolver in resolvers) {
+      if (resolver is EmbedderUriResolver) {
+        if (resolver.length > 0) {
+          return true;
+        }
+      }
+    }
+    return false;
+  }
+
   /**
    * Set up a [SourceFactory] that resolves packages as appropriate for the
    * given [disposition].
    */
   SourceFactory _createSourceFactory(FolderDisposition disposition) {
-    UriResolver dartResolver = new DartUriResolver(analysisServer.defaultSdk);
-    UriResolver resourceResolver = new ResourceUriResolver(resourceProvider);
     List<UriResolver> resolvers = [];
-    resolvers.add(dartResolver);
-    resolvers.addAll(disposition.createPackageUriResolvers(resourceProvider));
-    resolvers.add(resourceResolver);
+    List<UriResolver> packageUriResolvers =
+        disposition.createPackageUriResolvers(resourceProvider);
+    if (!_useEmbedderUriResolver(packageUriResolvers)) {
+      // If we aren't using the embedder uri resolver for dart: libraries,
+      // insert the default Dart SDK uri resolver.
+      resolvers.add(new DartUriResolver(analysisServer.defaultSdk));
+    }
+    resolvers.addAll(packageUriResolvers);
+    resolvers.add(new ResourceUriResolver(resourceProvider));
     return new SourceFactory(resolvers, disposition.packages);
   }
 }