Rename OS-specific MemoryPressureMonitor implementations.

chrome/browser/chromeos/memory/oom_priority_manager.cc

 // Copyright (c) 2012 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/chromeos/memory/oom_priority_manager.h"
 
 #include <algorithm>
 #include <set>
 #include <vector>
 
@@ skipping 494 matching lines @@
       if (!low_memory_observer_) {
         // Coming here we know that a renderer was just killed and memory should
         // come back into the pool. However - the memory pressure observer did
         // not yet update its status and therefore we ask it to redo the
         // measurement, calling us again if we have to release more.
         // Note: We do not only accelerate the discarding speed by doing another
         // check in short succession - we also accelerate it because the timer
         // driven MemoryPressureMonitor will continue to produce timed events
         // on top. So the longer the cleanup phase takes, the more tabs will
         // get discarded in parallel.
-        base::MemoryPressureMonitorChromeOS* monitor =
-            static_cast<base::MemoryPressureMonitorChromeOS*>(
+        base::chromeos::MemoryPressureMonitor* monitor =

[grt (UTC plus 2), 2015/05/14 14:07:40]

since you're editing the world, what do you think about putting a public static
Get() method on base::chromeos::MemoryPressureMonitor that does the casting so
that client code like this doesn't need to do it?

[chrisha, 2015/05/14 15:27:17]

base::MemoryPressureMonitor::Get returns a pointer to the singleton
base::MemoryPressureMonitor. Because of the current derivation layout, this is
actually one of a base::win::MPM, base::chromeos::MPM or a base::mac::MPM.
Making the base class aware of the derived-types is a bit of an anti-pattern.

This is also the *only* the only place where the cast happens, and it does so
because it wants access to a function that is platform implementation specific.

My next cleanup in this code will be to actually rearrange things to a single
class with platform-specific implementations, and no derivation. This will
obviate the need for casting entirely. (This cleanup will hopefully happen once
I convince the memory-pressure owners that this is a good idea.)

So, leave it as is for now?

[grt (UTC plus 2), 2015/05/14 15:30:26]

I was suggesting adding a public static Get() method to base::chromeos::MP that
does the exact call and cast that you find here. It amounts to the same thing
that's here now, but more friendly.

[chrisha, 2015/05/14 19:53:15]

Well you know, my skull is pretty thick :)

Done.

+            static_cast<base::chromeos::MemoryPressureMonitor*>(
                 base::MemoryPressureMonitor::Get());
         if (monitor)
           monitor->ScheduleEarlyCheck();
       }
       break;
     }
     case content::NOTIFICATION_RENDER_WIDGET_VISIBILITY_CHANGED: {
       bool visible = *content::Details<bool>(details).ptr();
       if (visible) {
         content::RenderProcessHost* render_host =
@@ skipping 173 matching lines @@
   // For the moment we only do something when we reach a critical state.
   if (memory_pressure_level ==
       base::MemoryPressureListener::MEMORY_PRESSURE_LEVEL_CRITICAL) {
     LogMemoryAndDiscardTab();
   }
   // TODO(skuhne): If more memory pressure levels are introduced, we might
   // consider to call PurgeBrowserMemory() before CRITICAL is reached.
 }
 
 }  // namespace chromeos