Move purging memory from OnMemoryStateChange() to OnPurgeMemory() in discardable_memory

components/discardable_memory/service/discardable_shared_memory_manager.cc

Index: components/discardable_memory/service/discardable_shared_memory_manager.cc
diff --git a/components/discardable_memory/service/discardable_shared_memory_manager.cc b/components/discardable_memory/service/discardable_shared_memory_manager.cc
index a974b2d9e27d8f35d1a59a9fcc7a5e8fdfc6e0e0..f79c18f0910d5d591d197017ab68f23a930a7a7c 100644
--- a/components/discardable_memory/service/discardable_shared_memory_manager.cc
+++ b/components/discardable_memory/service/discardable_shared_memory_manager.cc
@@ -405,12 +405,14 @@ size_t DiscardableSharedMemoryManager::GetBytesAllocated() {
 
 void DiscardableSharedMemoryManager::OnMemoryStateChange(
     base::MemoryState state) {
+  // Don't use SetMemoryLimit() as it free up existing allocations.

[bashi, 2017/02/07 02:42:22]

As noted in
https://cs.chromium.org/chromium/src/base/memory/memory_coordinator_client.h?...,
we don't have to free up existing allocation on state change. OnPurgeMemory() is
called as needed.

[reveman, 2017/02/07 03:34:07]

nit: s/free/frees/

maybe also mention here that OnPurgeMemory() is called to actually free up
memory.

[bashi, 2017/02/07 04:31:35]

Done.

+  base::AutoLock lock(lock_);
   switch (state) {
     case base::MemoryState::NORMAL:
-      SetMemoryLimit(default_memory_limit_);
+      memory_limit_ = default_memory_limit_;
       break;
     case base::MemoryState::THROTTLED:
-      SetMemoryLimit(0);
+      memory_limit_ = 0;
       break;
     case base::MemoryState::SUSPENDED:
     // Note that SUSPENDED never occurs in the main browser process so far.
@@ -421,6 +423,11 @@ void DiscardableSharedMemoryManager::OnMemoryStateChange(
   }
 }
 
+void DiscardableSharedMemoryManager::OnPurgeMemory() {
+  base::AutoLock lock(lock_);
+  ReduceMemoryUsageUntilWithinLimit(0);
+}
+
 void DiscardableSharedMemoryManager::AllocateLockedDiscardableSharedMemory(
     int client_id,
     size_t size,