Fixes for URI and Object completions with the new driver.

pkg/analysis_server/lib/src/provisional/completion/dart/completion_dart.dart

Index: pkg/analysis_server/lib/src/provisional/completion/dart/completion_dart.dart
diff --git a/pkg/analysis_server/lib/src/provisional/completion/dart/completion_dart.dart b/pkg/analysis_server/lib/src/provisional/completion/dart/completion_dart.dart
index b25375adc6b95269dfc3ff38a9556c10c5abf4f0..bec47b407f53bb8b4fbe6f284febdab50be6b5ac 100644
--- a/pkg/analysis_server/lib/src/provisional/completion/dart/completion_dart.dart
+++ b/pkg/analysis_server/lib/src/provisional/completion/dart/completion_dart.dart
@@ -100,6 +100,11 @@ abstract class DartCompletionRequest extends CompletionRequest {
   DartType get objectType;
 
   /**
+   * Return the [SourceFactory] of the request.
+   */
+  SourceFactory get sourceFactory;
+
+  /**
    * Return the completion target.  This determines what part of the parse tree
    * will receive the newly inserted text.
    * At a minimum, all declarations in the completion scope in [target.unit]