PlzNavigate: Eliminate test_runner bailing out of layout tests too early

components/test_runner/test_runner.h

Index: components/test_runner/test_runner.h
diff --git a/components/test_runner/test_runner.h b/components/test_runner/test_runner.h
index 69b2ea5fcdd2fc02d2e90a826b188b367354cb98..6f26a2237c5a0c41a714c99cd3e339f6ab320604 100644
--- a/components/test_runner/test_runner.h
+++ b/components/test_runner/test_runner.h
@@ -99,6 +99,8 @@ class TestRunner : public WebTestRunner {
   void SetFocus(blink::WebView* web_view, bool focus) override;
 
   // Methods used by WebViewTestClient and WebFrameTestClient.
+  void OnNavigationBegin(blink::WebFrame* frame);
+  void OnNavigationEnd() { will_navigate_ = false; }
   void OnAnimationScheduled(blink::WebWidget* widget);
   void OnAnimationBegun(blink::WebWidget* widget);
   std::string GetAcceptLanguages() const;
@@ -614,6 +616,12 @@ class TestRunner : public WebTestRunner {
 
   bool use_mock_theme_;
 
+  // This is true in the period between the start of a navigation and when the
+  // provisional load for that navigation is started. Note that when
+  // browser-side navigation is enabled there is an arbitrary gap between these
+  // two events.
+  bool will_navigate_;
+
   std::unique_ptr<MockCredentialManagerClient> credential_manager_client_;
   std::unique_ptr<MockScreenOrientationClient> mock_screen_orientation_client_;
   std::unique_ptr<MockWebSpeechRecognizer> speech_recognizer_;