[Sessions] Add detailed logging of SessionRestore events.

chrome/browser/sessions/tab_loader.cc

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "chrome/browser/sessions/tab_loader.h"
 
 #include <algorithm>
 #include <string>
 
+#include "base/metrics/field_trial.h"
 #include "base/metrics/histogram.h"
 #include "base/strings/stringprintf.h"
 #include "chrome/browser/ui/browser.h"
 #include "chrome/browser/ui/browser_finder.h"
 #include "chrome/browser/ui/tabs/tab_strip_model.h"
 #include "content/public/browser/navigation_controller.h"
 #include "content/public/browser/notification_service.h"
 #include "content/public/browser/notification_types.h"
 #include "content/public/browser/render_widget_host.h"
 #include "content/public/browser/render_widget_host_view.h"
+#include "content/public/browser/session_restore_uma.h"
 #include "content/public/browser/web_contents.h"
 
 using content::NavigationController;
 using content::RenderWidgetHost;
 using content::WebContents;
 
 void TabLoader::Observe(int type,
                         const content::NotificationSource& source,
                         const content::NotificationDetails& details) {
   switch (type) {
@@ skipping 80 matching lines @@
 
 void TabLoader::LoadNextTab() {
   // LoadNextTab should only get called after we have started the tab
   // loading.
   CHECK(delegate_);
   if (!tabs_to_load_.empty()) {
     NavigationController* controller = tabs_to_load_.front();
     DCHECK(controller);
     tabs_loading_.insert(controller);
     tabs_to_load_.pop_front();
+
+    // Keep track of tabs that have been automatically loaded by session
+    // restore. This is the complement to SessionRestore.DeferredTabLoadedByUser
+    // recorded in NavigationControllerImpl::SetActive.
+    if (controller->NeedsReload()) {
+      UMA_HISTOGRAM_ENUMERATION(
+          content::kSessionRestoreTabActions,
+          content::kSessionRestoreTabActionsUma_BackgroundTabLoaded,
+          content::kSessionRestoreTabActionsUma_Max);
+    }
+
     controller->LoadIfNecessary();
     content::WebContents* contents = controller->GetWebContents();
     if (contents) {
       Browser* browser = chrome::FindBrowserWithWebContents(contents);
       if (browser &&
           browser->tab_strip_model()->GetActiveWebContents() != contents) {
         // By default tabs are marked as visible. As only the active tab is
         // visible we need to explicitly tell non-active tabs they are hidden.
         // Without this call non-active tabs are not marked as backgrounded.
         //
@@ skipping 46 matching lines @@
 }
 
 void TabLoader::HandleTabClosedOrLoaded(NavigationController* controller) {
   RemoveTab(controller);
   if (delegate_ && loading_enabled_)
     LoadNextTab();
 }
 
 void TabLoader::OnMemoryPressure(
     base::MemoryPressureListener::MemoryPressureLevel memory_pressure_level) {
+  // On Windows and Mac this mechanism is only experimentally enabled.
+#if defined(OS_WIN) or (defined(OS_MACOSX) and !defined(OS_IOS))
+  // If memory pressure isn't explicitly turned on then ignore these calls.
+  std::string react_to_memory_pressure = variations::GetVariationParamValue(
+      kSessionRestoreBackgroundLoading, "ReactToMemoryPressure"));
+  if (react_to_memory_pressure != "1")
+    return;
+#endif
+
+  // Note that the session restore was interrupted by memory pressure.
+  UMA_HISTOGRAM_ENUMERATION(
+          content::kSessionRestoreActions,
+          content::kSessionRestoreActionsUma_InterruptedByMemoryPressure,
+          content::kSessionRestoreActionsUma_Max);
+
   // When receiving a resource pressure level warning, we stop pre-loading more
   // tabs since we are running in danger of loading more tabs by throwing out
   // old ones.
   if (tabs_to_load_.empty())
     return;
   // Stop the timer and suppress any tab loads while we clean the list.
   SetTabLoadingEnabled(false);
   while (!tabs_to_load_.empty()) {
+    // Count the number of tabs that have had their loading deferred.
+    UMA_HISTOGRAM_ENUMERATION(
+        content::kSessionRestoreTabActions,
+        content::kSessionRestoreTabActionsUma_TabLoadingDeferred,
+        content::kSessionRestoreTabActionsUma_Max);
+
     NavigationController* controller = tabs_to_load_.front();
     tabs_to_load_.pop_front();
     RemoveTab(controller);
   }
   // By calling |LoadNextTab| explicitly, we make sure that the
   // |NOTIFICATION_SESSION_RESTORE_DONE| event gets sent.
   LoadNextTab();
 }
 
 // static
 TabLoader* TabLoader::shared_tab_loader_ = nullptr;