Added support for GN workspaces.

pkg/analyzer/lib/src/context/builder.dart

Index: pkg/analyzer/lib/src/context/builder.dart
diff --git a/pkg/analyzer/lib/src/context/builder.dart b/pkg/analyzer/lib/src/context/builder.dart
index aad53cfdde47479da00382605de164cd7c689fcc..b308352e723db7c9e34ae3b682162ddf8fa2593d 100644
--- a/pkg/analyzer/lib/src/context/builder.dart
+++ b/pkg/analyzer/lib/src/context/builder.dart
@@ -17,6 +17,7 @@ import 'package:analyzer/src/command_line/arguments.dart'
 import 'package:analyzer/src/dart/sdk/sdk.dart';
 import 'package:analyzer/src/generated/bazel.dart';
 import 'package:analyzer/src/generated/engine.dart';
+import 'package:analyzer/src/generated/gn.dart';
 import 'package:analyzer/src/generated/sdk.dart';
 import 'package:analyzer/src/generated/source.dart';
 import 'package:analyzer/src/summary/package_bundle_reader.dart';
@@ -208,6 +209,17 @@ class ContextBuilder {
       return new SourceFactory(resolvers, null, resourceProvider);
     }
 
+    GnWorkspace gnWorkspace = GnWorkspace.find(resourceProvider, rootPath);
+    if (gnWorkspace != null) {
+      DartSdk sdk = findSdk(gnWorkspace.packageMap, options);
+      List<UriResolver> resolvers = <UriResolver>[
+        new DartUriResolver(sdk),
+        new GnPackageUriResolver(gnWorkspace),
+        new GnFileUriResolver(gnWorkspace)
+      ];
+      return new SourceFactory(resolvers, null, resourceProvider);
+    }
+
     Packages packages = createPackageMap(rootPath);
     Map<String, List<Folder>> packageMap = convertPackagesToMap(packages);
     List<UriResolver> resolvers = <UriResolver>[