Place SessionRestore/MemoryPressure interactions behind a field trial on Mac/Win platforms.

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/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 "components/favicon/content/content_favicon_driver.h"
+#include "components/variations/variations_associated_data.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/web_contents.h"
 
 using content::NavigationController;
 using content::RenderWidgetHost;
 using content::WebContents;
@@ skipping 162 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) || (defined(OS_MACOSX) && !defined(OS_IOS))
+  // If memory pressure integration isn't explicitly enabled then ignore these
+  // calls.
+  std::string react_to_memory_pressure = variations::GetVariationParamValue(
+      "IntelligentSessionRestore", "ReactToMemoryPressure");
+  if (react_to_memory_pressure != "true")
+    return;
+#endif
+
   // 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()) {
     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;