Provide renderers with memory pressure signals.

content/browser/memory/memory_pressure_controller_impl.h

Index: content/browser/memory/memory_pressure_controller_impl.h
diff --git a/content/browser/memory/memory_pressure_controller.h b/content/browser/memory/memory_pressure_controller_impl.h
similarity index 52%
rename from content/browser/memory/memory_pressure_controller.h
rename to content/browser/memory/memory_pressure_controller_impl.h
index f81540957d7b416f1b268e7e63280b14268ceb31..3a66c683fb93f3b142655d9b84e77e239700fd00 100644
--- a/content/browser/memory/memory_pressure_controller.h
+++ b/content/browser/memory/memory_pressure_controller_impl.h
@@ -2,8 +2,8 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-#ifndef CONTENT_BROWSER_MEMORY_MEMORY_PRESSURE_CONTROLLER_H_
-#define CONTENT_BROWSER_MEMORY_MEMORY_PRESSURE_CONTROLLER_H_
+#ifndef CONTENT_BROWSER_MEMORY_MEMORY_PRESSURE_CONTROLLER_IMPL_H_
+#define CONTENT_BROWSER_MEMORY_MEMORY_PRESSURE_CONTROLLER_IMPL_H_
 
 #include <map>
 
@@ -19,33 +19,55 @@ class BrowserChildProcessHost;
 class MemoryMessageFilter;
 class RenderProcessHost;
 
-class CONTENT_EXPORT MemoryPressureController {
+// Controller for memory pressure IPC messages. Each child process owns and
+// registers a MemoryMessageFilter, which can be used to both suppress and
+// simulate memory pressure messages across processes. This controller
+// coordinates suppressing and simulation of messages, as well as allows for
+// messages to be forward to individual processes. This allows the browser

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

nit: forwarded

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

Done.

+// process to control what memory pressure messages are seen in child processes.
+// For more details see content/browser/memory/memory_message_filter.h and
+// content/child/memory/child_memory_message_filter.h.
+class CONTENT_EXPORT MemoryPressureControllerImpl {

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

It'd be more common to have this derive from MemoryPressureController and
override the public methods, but I can see that doesn't work as well with your
singleton approach.  This should be fine.

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

Yeah... I wasn't 100% sure whether or not this was the way to go.

  public:
   // These methods must be called on the IO thread.
   void OnMemoryMessageFilterAdded(MemoryMessageFilter* filter);
   void OnMemoryMessageFilterRemoved(MemoryMessageFilter* filter);
 
   // These methods can be called from any thread.
+
+  // Suppresses all memory pressure messages from passing through all attached
+  // MemoryMessageFilters. Any messages sent through a "suppressed" filter will
+  // be ignored on the receiving end.
   void SetPressureNotificationsSuppressedInAllProcesses(bool suppressed);
+
+  // Simulates memory pressure in all processes by invoking
+  // SimulatePressureNotification on all attached MemoryMessageFilters. These
+  // messages will be received even if suppression is enabled.
   void SimulatePressureNotificationInAllProcesses(
       base::MemoryPressureListener::MemoryPressureLevel level);
+
+  // Sends a memory pressure notification to the specified browser child process
+  // via its attached MemoryMessageFilter.
   void SendPressureNotification(
       const BrowserChildProcessHost* child_process_host,
       base::MemoryPressureListener::MemoryPressureLevel level);
+
+  // Sends a memory pressure notification to the specified renderer process via
+  // its attached MemoryMessageFilter.
   void SendPressureNotification(
       const RenderProcessHost* render_process_host,
       base::MemoryPressureListener::MemoryPressureLevel level);
 
   // This method can be called from any thread.
-  static MemoryPressureController* GetInstance();
+  static MemoryPressureControllerImpl* GetInstance();

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

nit: Move this to be the first public method.

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

Done.

 
  protected:
-  virtual ~MemoryPressureController();
+  virtual ~MemoryPressureControllerImpl();
 
  private:
-  friend struct base::DefaultSingletonTraits<MemoryPressureController>;
+  friend struct base::DefaultSingletonTraits<MemoryPressureControllerImpl>;
 
-  MemoryPressureController();
+  MemoryPressureControllerImpl();
 
   // Implementation of the various SendPressureNotification methods.
   void SendPressureNotificationImpl(
@@ -58,9 +80,9 @@ class CONTENT_EXPORT MemoryPressureController {
       MemoryMessageFilterMap;
   MemoryMessageFilterMap memory_message_filters_;
 
-  DISALLOW_COPY_AND_ASSIGN(MemoryPressureController);
+  DISALLOW_COPY_AND_ASSIGN(MemoryPressureControllerImpl);
 };
 
 }  // namespace content
 
-#endif  // CONTENT_BROWSER_MEMORY_MEMORY_PRESSURE_CONTROLLER_H_
+#endif  // CONTENT_BROWSER_MEMORY_MEMORY_PRESSURE_CONTROLLER_IMPL_H_