Provide renderers with memory pressure signals.

content/public/browser/memory_pressure_controller.h

Index: content/public/browser/memory_pressure_controller.h
diff --git a/content/public/browser/memory_pressure_controller.h b/content/public/browser/memory_pressure_controller.h
new file mode 100644
index 0000000000000000000000000000000000000000..86df6be2f8214666808952ee8a615e15f014d185
--- /dev/null
+++ b/content/public/browser/memory_pressure_controller.h
@@ -0,0 +1,34 @@
+// Copyright 2016 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.
+
+#ifndef CONTENT_PUBLIC_BROWSER_MEMORY_PRESSURE_CONTROLLER_H_
+#define CONTENT_PUBLIC_BROWSER_MEMORY_PRESSURE_CONTROLLER_H_
+
+#include "base/memory/memory_pressure_listener.h"
+#include "content/common/content_export.h"
+
+namespace content {
+
+class BrowserChildProcessHost;
+class RenderProcessHost;
+
+// Facade around the singleton MemoryPressureControllerImpl class defined in

[Charlie Reis, 2016/01/29 19:46:56]

We probably shouldn't introduce a public class in terms of its impl class, since
people working on content embedders shouldn't have to dig through our
implementations.

I'm ok leaving a reference to the impl.h file for more details, but maybe the
rest of the comment can be phrased in a more general way?

[chrisha, 2016/01/29 21:12:12]

Done.

+// content/browser/memory/memory_pressure_controller_impl.h. See that header for
+// more details. These are exposed so that chrome/browser can interact with the

[Charlie Reis, 2016/01/29 19:46:56]

Let's say "content embedders" rather than chrome/browser.

[chrisha, 2016/01/29 21:12:12]

Done.

+// content memory pressure subsystem. These may be called from any thread.
+class CONTENT_EXPORT MemoryPressureController {
+ public:
+  static void SendPressureNotification(

[Charlie Reis, 2016/01/29 19:46:56]

Let's copy the comments on these functions here, so that people don't have to
read the impl file unless they want to understand how it works.

[chrisha, 2016/01/29 21:12:12]

Done.

+      const BrowserChildProcessHost* child_process_host,
+      base::MemoryPressureListener::MemoryPressureLevel level);
+  static void SendPressureNotification(
+      const RenderProcessHost* render_process_host,
+      base::MemoryPressureListener::MemoryPressureLevel level);
+ private:

[Charlie Reis, 2016/01/29 19:46:56]

nit: Add blank line above.

[chrisha, 2016/01/29 21:12:13]

Done.

+  DISALLOW_COPY_AND_ASSIGN(MemoryPressureController);
+};
+
+}  // namespace content
+
+#endif  // CONTENT_PUBLIC_BROWSER_MEMORY_MEMORY_PRESSURE_CONTROLLER_H_

[Charlie Reis, 2016/01/29 19:46:56]

Looks like you have an extra MEMORY_ here.

[chrisha, 2016/01/29 21:12:12]

Indeed I do. Removed.