Update ThumbnailTest Frame Waiting

ThumbnailTest.ShouldCaptureOnNavigatingAwaySlowPageLoad was using a time based
wait, to simulate awaiting a frame submission. However the timing on viz debug
builds on Linux64 was leading to incorrect results.

This updates the test to use RenderFrameSubmissionObserver to wait directly upon
frame generation.

TEST=ThumbnailTest.ShouldCaptureOnNavigatingAwaySlowPageLoad

Bug: 843921
Change-Id: I71cd8acdc528a3b220c8ccbbbece585ed5cf03bd
Reviewed-on: https://chromium-review.googlesource.com/1097216Reviewed-by: Marc Treib <treib@chromium.org>
Commit-Queue: Jonathan Ross <jonross@chromium.org>
Cr-Commit-Position: refs/heads/master@{#566807}

chrome/browser/thumbnails/thumbnail_browsertest.cc

@@ -23,6 +23,7 @@
 #include "content/public/browser/navigation_handle.h"
 #include "content/public/browser/web_contents_observer.h"
 #include "content/public/common/content_switches.h"
+#include "content/public/test/browser_test_utils.h"
 #include "net/test/embedded_test_server/controllable_http_response.h"
 #include "net/test/embedded_test_server/embedded_test_server.h"
 #include "testing/gmock/include/gmock/gmock.h"
@@ -83,13 +84,6 @@ std::string MakeHtmlDocument(const std::string& background_color) {
       background_color.c_str());
 }
 
-void Sleep(base::TimeDelta delta) {
-  base::RunLoop run_loop;
-  base::ThreadTaskRunnerHandle::Get()->PostDelayedTask(
-      FROM_HERE, run_loop.QuitClosure(), delta);
-  run_loop.Run();
-}
-
 class MockThumbnailService : public ThumbnailService {
  public:
   MOCK_METHOD2(SetPageThumbnail,
@@ -323,10 +317,12 @@ IN_PROC_BROWSER_TEST_F(ThumbnailTest,
   // Navigate to the red page.
   ui_test_utils::NavigateToURL(browser(), red_url);
 
-  // Give the renderer process some time to actually paint it. Without this,
-  // there's a chance we might attempt to take a screenshot before the first
-  // paint, which would fail.
-  Sleep(base::TimeDelta::FromMilliseconds(200));
+  // Ensure that the updated WebContents has produced a frame after navigation.
+  // Without this, there's a chance we might attempt to take a screenshot before
+  // the first paint, which would fail.
+  content::RenderFrameSubmissionObserver frame_observer(
+      browser()->tab_strip_model()->GetActiveWebContents());
+  frame_observer.WaitForMetadataChange();
 
   // Before navigating away from the red page, we should take a thumbnail.
   // Note that the page load is deliberately slowed down, so that the

testing/buildbot/filters/viz.browser_tests.filter

@@ -10,6 +10,3 @@
 
 # Mac Flaking with missing browser. https://crbug.com/842664
 -IndependentOTRProfileManagerTest.DeleteImmediatelyWhenBrowsersAlreadyClosed
-
-# https://crbug.com/843921
--ThumbnailTest.ShouldCaptureOnNavigatingAwaySlowPageLoad