Load restored tab when thumbnail is requested

Fixed: 1123994
Change-Id: I0f099ad8196ba2a967327bca569b535b0585e9f2
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2388761
Commit-Queue: Collin Baker <collinbaker@chromium.org>
Reviewed-by: Dana Fried <dfried@chromium.org>
Reviewed-by: François Doray <fdoray@chromium.org>
Cr-Commit-Position: refs/heads/master@{#804216}

chrome/browser/ui/thumbnails/thumbnail_tab_helper.cc

@@ -175,6 +175,8 @@ class ThumbnailTabHelper::TabStateTracker
   // ThumbnailImage::Delegate:
   void ThumbnailImageBeingObservedChanged(bool is_being_observed) override {
     capture_driver_.UpdateThumbnailVisibility(is_being_observed);
+    if (is_being_observed)
+      web_contents()->GetController().LoadIfNecessary();
   }
 
   void PageReadinessChanged(PageReadiness readiness) {

chrome/browser/ui/thumbnails/thumbnail_tab_helper_browsertest.cc

@@ -5,6 +5,7 @@
 #include "base/optional.h"
 #include "base/test/scoped_feature_list.h"
 #include "build/build_config.h"
+#include "chrome/browser/resource_coordinator/session_restore_policy.h"
 #include "chrome/browser/sessions/tab_loader_tester.h"
 #include "chrome/browser/ui/browser.h"
 #include "chrome/browser/ui/browser_commands.h"
@@ -77,9 +78,10 @@ class ThumbnailTabHelperBrowserTest : public InProcessBrowserTest {
   }
 
 #if BUILDFLAG(ENABLE_SESSION_SERVICE)
-  void SetMaxSimultaneousLoadsForTesting(TabLoader* tab_loader) {
+  void ConfigureTabLoader(TabLoader* tab_loader) {
     TabLoaderTester tester(tab_loader);
     tester.SetMaxSimultaneousLoadsForTesting(1);
+    tester.SetMaxLoadedTabCountForTesting(1);
   }
 #endif
 
@@ -172,14 +174,10 @@ IN_PROC_BROWSER_TEST_F(ThumbnailTabHelperBrowserTest,
 // with ENABLE_SESSION_SERVICE.
 #if BUILDFLAG(ENABLE_SESSION_SERVICE)
 
-// Note that this code is mostly cribbed from the test:
-//   TabRestoreTest.TabsFromRestoredWindowsAreLoadedGradually
-// because we need to simulate a browser restore that doesn't reload all of the
-// tabs - and then ensure that we do get thumbnails when we watch the tabs that
-// didn't load.
-IN_PROC_BROWSER_TEST_F(
-    ThumbnailTabHelperBrowserTest,
-    WatchingThumbnailAfterBrowserRestoreCausesPageLoadAndProducesThumbnail) {
+// On browser restore, some tabs may not be loaded. Requesting a
+// thumbnail for one of these tabs should trigger load and capture.
+IN_PROC_BROWSER_TEST_F(ThumbnailTabHelperBrowserTest,
+                       CapturesRestoredTabWhenRequested) {
   ui_test_utils::NavigateToURLWithDisposition(
       browser(), url2_, WindowOpenDisposition::NEW_WINDOW,
       ui_test_utils::BROWSER_TEST_WAIT_FOR_BROWSER);
@@ -191,11 +189,10 @@ IN_PROC_BROWSER_TEST_F(
   EXPECT_EQ(kTabCount, browser2->tab_strip_model()->count());
   CloseBrowserSynchronously(browser2);
 
-  // When the tab loader is created configure it for this test. This ensures
-  // that no more than 1 loading slot is used for the test.
-  base::RepeatingCallback<void(TabLoader*)> callback = base::BindRepeating(
-      &ThumbnailTabHelperBrowserTest::SetMaxSimultaneousLoadsForTesting,
-      base::Unretained(this));
+  // Set up the tab loader to ensure tabs are left unloaded.
+  base::RepeatingCallback<void(TabLoader*)> callback =
+      base::BindRepeating(&ThumbnailTabHelperBrowserTest::ConfigureTabLoader,
+                          base::Unretained(this));
   TabLoaderTester::SetConstructionCallbackForTesting(&callback);
 
   // Restore recently closed window.
@@ -205,18 +202,6 @@ IN_PROC_BROWSER_TEST_F(
 
   EXPECT_EQ(kTabCount, browser2->tab_strip_model()->count());
   EXPECT_EQ(kTabCount - 1, browser2->tab_strip_model()->active_index());
-  // These two tabs should be loaded by TabLoader.
-  EnsureTabLoaded(browser2->tab_strip_model()->GetWebContentsAt(kTabCount - 1));
-  EnsureTabLoaded(browser2->tab_strip_model()->GetWebContentsAt(0));
-
-  // The following isn't necessary but just to be sure there is no any async
-  // task that could have an impact on the expectations below. Note that because
-  // we're on the browser main thread, tasks are executed in order, so this
-  // effectively flushes the queue.
-  base::RunLoop run_loop;
-  base::ThreadTaskRunnerHandle::Get()->PostTask(FROM_HERE,
-                                                run_loop.QuitClosure());
-  run_loop.Run();
 
   // These tabs shouldn't want to be loaded.
   for (int tab_idx = 1; tab_idx < kTabCount - 1; ++tab_idx) {