Run lifecycle updates only (but not begin frames) when in nested composite

It isn't necessary to run BeginFrame and all of the UpdateVisualState
code. This should make it easier to move LayerTreeView into blink.

Change-Id: Iefb0caffc6cdc38db10352b50404afebb8120dd0
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2110512Reviewed-by: Avi Drissman <avi@chromium.org>
Commit-Queue: Dave Tapuska <dtapuska@chromium.org>
Cr-Commit-Position: refs/heads/master@{#751802}

content/shell/test_runner/web_widget_test_proxy.cc

@@ -202,8 +202,8 @@ void WebWidgetTestProxy::SynchronouslyComposite(bool do_raster) {
     // Web tests can use a nested message loop to pump frames while inside a
     // frame, but the compositor does not support this. In this case, we only
     // run blink's lifecycle updates.
-    BeginMainFrame(base::TimeTicks::Now());
-    UpdateVisualState();
+    GetWebWidget()->UpdateAllLifecyclePhases(
+        blink::DocumentUpdateReason::kTest);
     return;
   }