Rename OS-specific MemoryPressureMonitor implementations.

chrome/browser/chromeos/memory/oom_priority_manager.cc

Index: chrome/browser/chromeos/memory/oom_priority_manager.cc
diff --git a/chrome/browser/chromeos/memory/oom_priority_manager.cc b/chrome/browser/chromeos/memory/oom_priority_manager.cc
index 38e2dafe2a4968774e77588de12890ed2601ac4d..a934e115ec5ddf1ff5254f4418a2c2a2b3f5ef45 100644
--- a/chrome/browser/chromeos/memory/oom_priority_manager.cc
+++ b/chrome/browser/chromeos/memory/oom_priority_manager.cc
@@ -512,8 +512,8 @@ void OomPriorityManager::Observe(int type,
         // 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();