base: Add soft memory limit to DiscardableMemoryManager.

base/memory/discardable_memory_android.cc

Index: base/memory/discardable_memory_android.cc
diff --git a/base/memory/discardable_memory_android.cc b/base/memory/discardable_memory_android.cc
index c3de3a36b3d9bac3fa8d035dd7eb8fad7891c400..c929a8768434ea973520244182db1535342aa689 100644
--- a/base/memory/discardable_memory_android.cc
+++ b/base/memory/discardable_memory_android.cc
@@ -32,7 +32,10 @@ size_t GetOptimalAshmemRegionSizeForAllocator() {
 // Holds the shared state used for allocations.
 struct SharedState {
   SharedState()
-      : manager(kAshmemMemoryLimit, kAshmemMemoryLimit),
+      : manager(kAshmemMemoryLimit,
+                kAshmemMemoryLimit,
+                kAshmemMemoryLimit,
+                TimeDelta::Max()),
         allocator(kAshmemAllocatorName,
                   GetOptimalAshmemRegionSizeForAllocator()) {}
 
@@ -54,6 +57,11 @@ void DiscardableMemory::UnregisterMemoryPressureListeners() {
 }
 
 // static
+bool DiscardableMemory::IdleNotification() {
+  return internal::DiscardableMemoryEmulated::IdleNotification();

[Stephen White, 2014/06/20 14:06:01]

Not new to this patch, but it seems odd to have the discardable memory
implementions fall back to the emulated implementation for these methods. Maybe
they should be refactored to a common base class instead
(DiscardableMemoryBase?).

[reveman, 2014/06/20 18:06:28]

It's not really a fallback. IdleNotification will notify all implementations
that care about this signal. Just happens that "emulated" is the only
implementation that care right now. If ashmem implementation starts taking
advantage of this notification in the future, we'd call
internal::DiscardableMemoryAshmem::IdleNotification() too and only return true
if both functions return true.

FYI, we typically don't use more than one type discardable memory implementation
except for unit tests but there's nothing stopping us from using multiple if
that would ever be useful.

+}
+
+// static
 void DiscardableMemory::GetSupportedTypes(
     std::vector<DiscardableMemoryType>* types) {
   const DiscardableMemoryType supported_types[] = {