Fix WebViewTest.SetBaseBackgroundColorBeforeMainFrame failure with NULL WebAgentGroupScheduler

Before this CL, `out/Default/blink_unittests --single-process-tests` was failing. This is because even though WebViewHelper creates AgentGroupScheduler, the tests created another AgentGroupScheduler.

This CL fixes this problem.

Bug: 1166542, 1105403
Change-Id: I96cf2e43896d0c6ac706d3bdd354647b12d4c8db
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2629149Reviewed-by: Kentaro Hara <haraken@chromium.org>
Reviewed-by: Kouhei Ueno <kouhei@chromium.org>
Commit-Queue: Minoru Chikamune <chikamune@chromium.org>
Cr-Commit-Position: refs/heads/master@{#843833}

third_party/blink/renderer/core/exported/web_view_test.cc

@@ -480,17 +480,13 @@ TEST_F(WebViewTest, SetBaseBackgroundColorBeforeMainFrame) {
   // Note: this test doesn't use WebViewHelper since it intentionally runs
   // initialization code between WebView and WebLocalFrame creation.
   frame_test_helpers::TestWebViewClient web_view_client;
-  std::unique_ptr<blink::scheduler::WebAgentGroupScheduler>
-      agent_group_scheduler =
-          blink::scheduler::WebThreadScheduler::MainThreadScheduler()
-              ->CreateAgentGroupScheduler();
   WebViewImpl* web_view = static_cast<WebViewImpl*>(
       WebView::Create(&web_view_client,
                       /*is_hidden=*/false,
                       /*is_inside_portal=*/false,
                       /*compositing_enabled=*/true,
                       /*opener=*/nullptr, mojo::NullAssociatedReceiver(),
-                      *agent_group_scheduler));
+                      web_view_helper_.GetAgentGroupScheduler()));
 
   EXPECT_NE(SK_ColorBLUE, web_view->BackgroundColor());
   // WebView does not have a frame yet, but we should still be able to set the
@@ -2715,14 +2711,11 @@ ExternalDateTimeChooser* WebViewTest::GetExternalDateTimeChooser(
 TEST_F(WebViewTest, ClientTapHandlingNullWebViewClient) {
   // Note: this test doesn't use WebViewHelper since WebViewHelper creates an
   // internal WebViewClient on demand if the supplied WebViewClient is null.
-  std::unique_ptr<blink::scheduler::WebAgentGroupScheduler>
-      agent_group_scheduler =
-          blink::scheduler::WebThreadScheduler::MainThreadScheduler()
-              ->CreateAgentGroupScheduler();
   WebViewImpl* web_view = static_cast<WebViewImpl*>(WebView::Create(
       /*client=*/nullptr, /*is_hidden=*/false, /*is_inside_portal=*/false,
       /*compositing_enabled=*/false, /*opener=*/nullptr,
-      mojo::NullAssociatedReceiver(), *agent_group_scheduler));
+      mojo::NullAssociatedReceiver(),
+      web_view_helper_.GetAgentGroupScheduler()));
   frame_test_helpers::TestWebFrameClient web_frame_client;
   WebLocalFrame* local_frame =
       WebLocalFrame::CreateMainFrame(web_view, &web_frame_client, nullptr,

third_party/blink/renderer/core/frame/frame_test_helpers.h

@@ -452,6 +452,10 @@ class WebViewHelper : public ScopedMockOverlayScrollbars {
         is_for_child_local_root, is_for_nested_main_frame);
   }
 
+  blink::scheduler::WebAgentGroupScheduler& GetAgentGroupScheduler() {
+    return *agent_group_scheduler_;
+  }
+
  private:
   void InitializeWebView(TestWebViewClient*,
                          class WebView* opener);