[SessionRestore] Ignore WebContents that are not managed by TabLoader.

PageSignalReceiver dispatches page signals to every PageSignalObserver with
WebContents, thus, TabLoader will be notified with WebContents that is not
managed by TabLoader, causing crash when TabLoader tries to remove it from
notification registrar. This patch adds check inside OnPageAlmostIdle to ignore
WebContents that is not managed by TabLoader, as well as a unit test.

BUG=788744

Change-Id: If19d3b3ee9d73b932644c0574dc3b381eba3f232
Reviewed-on: https://chromium-review.googlesource.com/801655
Commit-Queue: lpy <lpy@chromium.org>
Reviewed-by: Scott Violet <sky@chromium.org>
Reviewed-by: Zhen Wang <zhenw@chromium.org>
Cr-Commit-Position: refs/heads/master@{#520706}

chrome/browser/sessions/tab_loader.cc

@@ -63,7 +63,13 @@ void TabLoader::Observe(int type,
 }
 
 void TabLoader::OnPageAlmostIdle(content::WebContents* web_contents) {
-  HandleTabClosedOrLoaded(&web_contents->GetController());
+  auto* controller = &web_contents->GetController();
+  // The |web_contents| is not managed by TabLoader.
+  if (tabs_loading_.find(controller) == tabs_loading_.end() &&
+      !base::ContainsValue(tabs_to_load_, controller)) {
+    return;
+  }
+  HandleTabClosedOrLoaded(controller);
 }
 
 void TabLoader::SetTabLoadingEnabled(bool enable_tab_loading) {

chrome/browser/sessions/tab_loader_unittest.cc

@@ -90,4 +90,13 @@ TEST_F(TabLoaderTest, UsePageAlmostIdleSignal) {
   EXPECT_TRUE(TabLoader::shared_tab_loader_->loading_enabled_);
   EXPECT_EQ(1u, TabLoader::shared_tab_loader_->tabs_loading_.size());
   EXPECT_EQ(0u, TabLoader::shared_tab_loader_->tabs_to_load_.size());
+
+  // |web_contents3| is not managed by TabLoader, thus it's ignored, and
+  // shouldn't cause loading state change or crash.
+  content::WebContents* web_contents3 =
+      test_web_contents_factory_->CreateWebContents(&testing_profile_);
+  TabLoader::shared_tab_loader_->OnPageAlmostIdle(web_contents3);
+  EXPECT_TRUE(TabLoader::shared_tab_loader_->loading_enabled_);
+  EXPECT_EQ(1u, TabLoader::shared_tab_loader_->tabs_loading_.size());
+  EXPECT_EQ(0u, TabLoader::shared_tab_loader_->tabs_to_load_.size());
 }