Re-land architecture for cross-process memory notification suppressing

content/browser/memory/memory_pressure_controller.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.h"
+
+#include "base/bind.h"
+#include "base/memory/memory_pressure_listener.h"
+#include "content/browser/memory/memory_message_filter.h"
+#include "content/public/browser/browser_thread.h"
+
+namespace content {
+
+MemoryPressureController::MemoryPressureController() {}
+
+MemoryPressureController::~MemoryPressureController() {}
+
+void MemoryPressureController::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(filter).second;
+  DCHECK(success);

[Sami, 2015/09/23 10:29:44]

This might complain about |success| not being used in release builds, but the
bots should tell us if that's a problem.

[petrcermak, 2015/09/23 10:32:37]

This pattern is used in other parts of the codebase and it should be fine
according to
https://code.google.com/p/chromium/codesearch#chromium/src/base/logging.h&l=656.

+
+  // 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 MemoryPressureController::OnMemoryMessageFilterRemoved(
+    MemoryMessageFilter* filter) {
+  DCHECK_CURRENTLY_ON(BrowserThread::IO);
+
+  // Remove the message filter from the set of all memory message filters and
+  // check that it was there beforehand.
+  const bool success = memory_message_filters_.erase(filter) == 1u;
+  DCHECK(success);
+}
+
+// static
+MemoryPressureController* MemoryPressureController::GetInstance() {
+  return base::Singleton<
+      MemoryPressureController,
+      base::LeakySingletonTraits<MemoryPressureController>>::get();
+}
+
+void MemoryPressureController::SetPressureNotificationsSuppressedInAllProcesses(
+    bool suppressed) {
+  if (!BrowserThread::CurrentlyOn(BrowserThread::IO)) {
+    // Note that passing base::Unretained(this) is safe here because the
+    // controller is a leaky singleton (i.e. it is never deleted).
+    BrowserThread::PostTask(
+        BrowserThread::IO, FROM_HERE,
+        base::Bind(&MemoryPressureController::
+                       SetPressureNotificationsSuppressedInAllProcesses,
+                   base::Unretained(this), suppressed));
+    return;
+  }
+
+  // Enable/disable suppressing memory notifications in the browser process.
+  base::MemoryPressureListener::SetNotificationsSuppressed(suppressed);
+
+  // Enable/disable suppressing memory notifications in all child processes.
+  for (MemoryMessageFilterSet::iterator it = memory_message_filters_.begin();
+       it != memory_message_filters_.end(); ++it) {
+    it->get()->SendSetPressureNotificationsSuppressed(suppressed);
+  }
+}
+
+}  // namespace content