gracefully degrade with response to client if fail to access client specified dart sdk

pkg/analysis_server/lib/src/domain_server.dart

Index: pkg/analysis_server/lib/src/domain_server.dart
diff --git a/pkg/analysis_server/lib/src/domain_server.dart b/pkg/analysis_server/lib/src/domain_server.dart
index 1e37f24a69a38d6fdacc023419823dcae5cafa84..4e18a53d5687b4b56f0321d1dc11914e527db5e2 100644
--- a/pkg/analysis_server/lib/src/domain_server.dart
+++ b/pkg/analysis_server/lib/src/domain_server.dart
@@ -109,8 +109,16 @@ class ServerDomainHandler implements RequestHandler {
     AnalysisContext context = AnalysisEngine.instance.createAnalysisContext();
     // TODO(brianwilkerson) Use the information from the request to set the
     // source factory in the context.
+    DirectoryBasedDartSdk sdk;
+    try {
+      sdk = new DirectoryBasedDartSdk(new JavaFile(sdkDirectory));
+    } on Exception catch (e) {
+      // TODO what error code should be returned here?

[Brian Wilkerson, 2014/03/05 22:48:09]

We should probably create a new error code to indicate what went wrong.
Otherwise clients can't inform their users.

[danrubel, 2014/03/05 23:27:13]

Done.

+      return new Response(request.id, new RequestError(
+          RequestError.CODE_INTERNAL_ERROR, 'Failed to access sdk: $e'));
+    }
     context.sourceFactory = new SourceFactory.con2([
-      new DartUriResolver(new DirectoryBasedDartSdk(new JavaFile(sdkDirectory))),
+      new DartUriResolver(sdk),
       new FileUriResolver(),
       // new PackageUriResolver(),
     ]);