Fixed incorrect comment docs for AwContentsIoThreadClient.

Bug: None
Change-Id: Iad4bf594dbc90c9e246d43fe9729e4b56fed9679
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1740128Reviewed-by: Richard Coles <torne@chromium.org>
Commit-Queue: Chris Mumford <cmumford@google.com>
Cr-Commit-Position: refs/heads/master@{#685220}

android_webview/browser/aw_contents_io_thread_client.h

@@ -89,7 +89,7 @@ class AwContentsIoThreadClient {
   // This will attempt to fetch the AwContentsIoThreadClient for the given
   // |render_process_id|, |render_frame_id| pair.
   // This method can be called from any thread.
-  // An empty scoped_ptr is a valid return value.
+  // A null std::unique_ptr is a valid return value.
   static std::unique_ptr<AwContentsIoThreadClient> FromID(int render_process_id,
                                                           int render_frame_id);
 
@@ -99,7 +99,7 @@ class AwContentsIoThreadClient {
       int frame_tree_node_id);
 
   // Returns the global thread client for service worker related callbacks.
-  // An empty scoped_ptr is a valid return value.
+  // A null std::unique_ptr is a valid return value.
   static std::unique_ptr<AwContentsIoThreadClient>
   GetServiceWorkerIoThreadClient();