Revert "Make TabLoader responsible for loading all tabs."

This reverts commit 94218d2c.

Reason for revert: Causing official build test failures.

BUG=865406

Original change's description:
> Make TabLoader responsible for loading all tabs.
> 
> Currently there's an inversion where active tabs in minimized windows don't get
> loaded as they are created. This is an optimization in the occlusion tracking code
> that doesn't calls ReloadIfNecessary unless the window hosting the active tab
> actually becomes visible. Due to this inversion the TabLoader can start loading
> background tabs in the minimized window before the active tab in the minimized
> window is ever loaded.
> 
> Giving TabLoader responsibility to load all tabs fixes this. In the case of
> active and visible tabs whose loads are initiated by the browser this is fine
> because calling ReloadIfNecessary twice is effectively a nop, and the TabLoader
> is already smart enough to track tabs that have started loading for external
> reasons.
> 
> BUG=864725
> 
> Change-Id: I4b86a71470b2cb1a1a9106c4d4d92ee6b18c7284
> Reviewed-on: https://chromium-review.googlesource.com/1141071
> Reviewed-by: Sébastien Marchand <sebmarchand@chromium.org>
> Commit-Queue: Chris Hamilton <chrisha@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#576071}

TBR=chrisha@chromium.org,sebmarchand@chromium.org

Change-Id: Icc2545c1a643042e44b15aa3fb4970045bdba105
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: 864725
Reviewed-on: https://chromium-review.googlesource.com/1143565Reviewed-by: Chris Hamilton <chrisha@chromium.org>
Commit-Queue: Chris Hamilton <chrisha@chromium.org>
Cr-Commit-Position: refs/heads/master@{#576494}

chrome/browser/sessions/session_restore.cc

@@ -657,6 +657,10 @@ class SessionRestoreImpl : public content::NotificationObserver {
         tab.extension_app_id, is_selected_tab, tab.pinned, true,
         last_active_time, session_storage_namespace.get(),
         tab.user_agent_override, true /* from_session_restore */);
+    // Regression check: if the current tab |is_selected_tab|, it should load
+    // immediately, otherwise, tabs should not start loading right away. The
+    // focused tab will be loaded by Browser, and TabLoader will load the rest.
+    DCHECK(is_selected_tab || web_contents->GetController().NeedsReload());
 
     // RestoreTab can return nullptr if |tab| doesn't have valid data.
     if (!web_contents)

chrome/browser/sessions/tab_loader.cc

@@ -207,7 +207,7 @@ void TabLoader::StartLoading(const std::vector<RestoredTab>& tabs) {
       }
     }
 
-    AddTab(restored_tab.contents());
+    AddTab(restored_tab.contents(), restored_tab.is_active());
   }
 
   StartTimerIfNeeded();
@@ -347,7 +347,7 @@ size_t TabLoader::GetMaxNewTabLoads() const {
   return tabs_to_load;
 }
 
-void TabLoader::AddTab(WebContents* contents) {
+void TabLoader::AddTab(WebContents* contents, bool loading_initiated) {
   DCHECK(reentry_depth_ > 0);  // This can only be called internally.
 
   // Handle tabs that have already started or finished loading.
@@ -360,7 +360,15 @@ void TabLoader::AddTab(WebContents* contents) {
     return;
   }
 
-  tabs_to_load_.push_back(contents);
+  // Otherwise place it in one of the |tabs_load_initiated_| or
+  // |tabs_to_load_| containers.
+  if (loading_initiated) {
+    delegate_->NotifyTabLoadStarted();
+    ++scheduled_to_load_count_;
+    tabs_load_initiated_.insert(contents);
+  } else {
+    tabs_to_load_.push_back(contents);
+  }
 }
 
 void TabLoader::RemoveTab(WebContents* contents) {

chrome/browser/sessions/tab_loader.h

@@ -127,7 +127,7 @@ class TabLoader : public base::RefCounted<TabLoader>,
 
   // Adds a tab that we are responsible for to one of the |tabs_*| containers.
   // Can invalidate self-destroy and timer invariants.
-  void AddTab(content::WebContents* contents);
+  void AddTab(content::WebContents* contents, bool loading_initiated);
 
   // Removes the tab from the set of tabs to load and list of tabs we're waiting
   // to get a load from. Can invalidate self-destroy and timer invariants.