Ensure test settings are fully reset between tests

Javascript can run after BlinkTestRunner::OnResetRendererAfterWebTest,
dirtying TestRunner state for the next test. A navigation to about:blank
is done after every test. This patch resets the TestRunner state after
the navigation to about:blank, when we are sure no test javascript can
change TestRunner state. This fixes a class of flaky bugs.

This behavior happened with video-overlay-scroll.html which would set a
custom layout dump (setCustomTextOutput) in a fullscreenchange event
handler. This event handler was not removed at the end of the test
(this will be fixed in a followup), and would run a second time, after
the custom text output setting was reset. This caused later tests to
run with custom text output from video-overlay-scroll.html. With this
patch, video-scrolled-iframe.html is no longer flaky.

Code in WebFrameTestProxy::BeginNavigation to intercept navigations
relied on TestRunner::PolicyDelegateEnabled being reset before it ran.
This patch now skips WebFrameTestProxy::BeginNavigation when the test
is not running.

Bug: 1048597
Change-Id: I888f7cc2ae91d7d3cfdd143a7573f62cb052c1cc
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2275348Reviewed-by: danakj <danakj@chromium.org>
Reviewed-by: Xianzhu Wang <wangxianzhu@chromium.org>
Commit-Queue: Philip Rogers <pdr@chromium.org>
Auto-Submit: Philip Rogers <pdr@chromium.org>
Cr-Commit-Position: refs/heads/master@{#784110}

content/shell/renderer/web_test/blink_test_runner.cc

@@ -465,6 +465,7 @@ void BlinkTestRunner::DidCommitNavigationInMainFrame() {
     return;
 
   waiting_for_reset_navigation_to_about_blank_ = false;
+  web_view_test_proxy_->test_interfaces()->ResetAll();
   GetWebTestControlHostRemote()->ResetRendererAfterWebTestDone();
 }
 
@@ -553,8 +554,10 @@ void BlinkTestRunner::OnResetRendererAfterWebTest() {
   // BlinkTestMsg_Reset should always be sent to the *current* view.
   DCHECK(web_view_test_proxy_->GetMainRenderFrame());
 
-  TestInterfaces* interfaces = web_view_test_proxy_->test_interfaces();
-  interfaces->ResetAll();
+  // Instead of resetting for the next test here, delay until after the
+  // navigation to about:blank (this is in |DidCommitNavigationInMainFrame()|).
+  // This ensures we reset settings that are set between now and the load of
+  // about:blank.
 
   // Navigating to about:blank will make sure that no new loads are initiated
   // by the renderer.

content/shell/renderer/web_test/web_frame_test_proxy.cc

@@ -478,6 +478,13 @@ void WebFrameTestProxy::WillSendRequest(blink::WebURLRequest& request) {
 
 void WebFrameTestProxy::BeginNavigation(
     std::unique_ptr<blink::WebNavigationInfo> info) {
+  // This check for whether the test is running ensures we do not intercept
+  // the about:blank navigation between tests.
+  if (!test_runner()->TestIsRunning()) {
+    RenderFrameImpl::BeginNavigation(std::move(info));
+    return;
+  }
+
   if (test_runner()->ShouldDumpNavigationPolicy()) {
     blink_test_runner()->PrintMessage(
         "Default policy for navigation to '" +