Use DiscardableMemoryManager on Android.

base/memory/discardable_memory.h

Index: base/memory/discardable_memory.h
diff --git a/base/memory/discardable_memory.h b/base/memory/discardable_memory.h
index 53d8d0e6f7c40b6b5d8d690a46b15158c4b4c0a5..eaeb8201d8c9e78c9f6cf7fe1013276491e20402 100644
--- a/base/memory/discardable_memory.h
+++ b/base/memory/discardable_memory.h
@@ -17,7 +17,7 @@ namespace base {
 
 enum DiscardableMemoryType {
   DISCARDABLE_MEMORY_TYPE_NONE,
-  DISCARDABLE_MEMORY_TYPE_ANDROID,
+  DISCARDABLE_MEMORY_TYPE_ASHMEM,
   DISCARDABLE_MEMORY_TYPE_MAC,
   DISCARDABLE_MEMORY_TYPE_EMULATED,
   DISCARDABLE_MEMORY_TYPE_MALLOC
@@ -117,11 +117,11 @@ class BASE_EXPORT DiscardableMemory {
 
   // Check whether a purge of all discardable memory in the system is supported.
   // Use only for testing!
-  static bool PurgeForTestingSupported();
+  static bool PurgeForTestingSupported(DiscardableMemoryType type);

[reveman, 2014/04/28 15:39:16]

How about we just remove PurgeForTestingSupported now that it's supported by all
types?

[Philippe, 2014/04/28 15:53:45]

I would be happy to do that but unfortunately the malloc type doesn't support
purging. I wasn't very comfortable with adding some extra global state keeping
track of the allocations just for testing but I can reconsider that. 

[reveman, 2014/04/28 16:02:24]

I think purging in the case of the malloc type is a NoOp. Everything that can be
purged is already purged.

 
   // Purge all discardable memory in the system. This call has global effects
   // across all running processes, so it should only be used for testing!
-  static void PurgeForTesting();
+  static void PurgeForTesting(DiscardableMemoryType type);

[reveman, 2014/04/28 15:39:16]

Can you explain why we need to pass a type here instead of just purging memory
for all supported types?

[Philippe, 2014/04/28 15:53:45]

Just to clarify, I was initially overriding the preferred type in the test
fixture and having PurgeForTesting() rely on the current global preferred type
but I was hitting a DCHECK() (which is quite valuable IMO) asserting that we are
setting the preferred type only once. So I thought it would be easier to avoid
messing up with the global state.

Does that make sense?

[reveman, 2014/04/28 16:02:24]

I agree that we shouldn't mess with preferred type here. It's just not clear to
me why PurgeForTesting can't look like this on Android:

PurgeForTesting {
  g_context.Pointer()->manager.PurgeAll();
  internal::DiscardableMemoryEmulated::PurgeForTesting();
}

[Philippe, 2014/04/28 16:31:21]

Yeah, good idea. I got rid of PurgeForTestingSupported().

 };
 
 }  // namespace base