Add an experiment to avoid memory pressure broadcasts.

content/browser/memory/memory_pressure_controller_impl.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 "content/browser/memory/memory_pressure_controller_impl.h"
 
 #include "base/bind.h"
+#include "base/feature_list.h"
 #include "content/browser/memory/memory_message_filter.h"
 #include "content/public/browser/browser_thread.h"
+#include "content/public/common/content_features.h"
+
+namespace features {
+
+// This experiment controls whether memory pressure notifications to
+// renderers are broadcast.
+const base::Feature kEnableBroadcastMemoryPressure = {
+    "EnableBroadcastMemoryPressure", base::FEATURE_ENABLED_BY_DEFAULT,
+};
+
+}  // namespace features
 
 namespace content {
 
 MemoryPressureControllerImpl::MemoryPressureControllerImpl() {}
 
 MemoryPressureControllerImpl::~MemoryPressureControllerImpl() {}
 
 void MemoryPressureControllerImpl::OnMemoryMessageFilterAdded(
     MemoryMessageFilter* filter) {
   DCHECK_CURRENTLY_ON(BrowserThread::IO);
 
   // Add the message filter to the set of all memory message filters and check
   // that it wasn't there beforehand.
   const bool success =
-      memory_message_filters_.insert(
-                                 std::make_pair(filter->process_host(), filter))
+      memory_message_filters_
+          .insert(std::make_pair(filter->process_host(), filter))
           .second;
   DCHECK(success);
 
   // There's no need to send a message to the child process if memory pressure
   // notifications are not suppressed.
   if (base::MemoryPressureListener::AreNotificationsSuppressed())
     filter->SendSetPressureNotificationsSuppressed(true);
 }
 
 void MemoryPressureControllerImpl::OnMemoryMessageFilterRemoved(
@@ skipping 84 matching lines @@
     BrowserThread::PostTask(
         BrowserThread::IO, FROM_HERE,
         base::Bind(&MemoryPressureControllerImpl::SendPressureNotificationImpl,
                    base::Unretained(this), child_process_host, level));
     return;
   }
 
   if (base::MemoryPressureListener::AreNotificationsSuppressed())
     return;
 
+// This desktop-only experiment can disable the memory pressure broadcasts.
+#if defined(OS_MACOSX) || (defined(OS_LINUX) && !defined(OS_CHROMEOS)) || \
+    defined(OS_WIN)
+  if (!base::FeatureList::IsEnabled(features::kEnableBroadcastMemoryPressure))
+    return;
+#endif
+
   // Find the appropriate message filter and dispatch the message.
   auto it = memory_message_filters_.find(child_process_host);
   if (it != memory_message_filters_.end())
     it->second->SendPressureNotification(level);
 }
 
 }  // namespace content