memory coordinator: Add trace macros to track state changes

base/memory/memory_coordinator_client.h

Index: base/memory/memory_coordinator_client.h
diff --git a/base/memory/memory_coordinator_client.h b/base/memory/memory_coordinator_client.h
index d63b17cc1f8b88779dfaa83b7a677529dbc37573..0a0dc368399bd71e0a614128d686b3fd4cd322dc 100644
--- a/base/memory/memory_coordinator_client.h
+++ b/base/memory/memory_coordinator_client.h
@@ -5,6 +5,9 @@
 #ifndef BASE_MEMORY_MEMORY_COORDINATOR_CLIENT_H_
 #define BASE_MEMORY_MEMORY_COORDINATOR_CLIENT_H_
 
+#include <stdint.h>
+#include <string>
+
 #include "base/base_export.h"
 
 namespace base {
@@ -22,7 +25,7 @@ namespace base {
 // MemoryState is an indicator that processes can use to guide their memory
 // allocation policies. For example, a process that receives the suspended
 // state can use that as as signal to drop memory caches.
-enum class MemoryState {
+enum class MemoryState : int32_t {

[haraken, 2016/11/01 04:20:29]

This change wouldn't be needed.

[bashi, 2016/11/01 05:02:16]

Done.

   // The state is unknown.
   UNKNOWN = -1,
   // No memory constraints.
@@ -38,6 +41,9 @@ enum class MemoryState {
   SUSPENDED = 2,
 };
 
+// Returns a string representation of MemoryState.
+BASE_EXPORT std::string MemoryStateToString(MemoryState state);

[dcheng, 2016/11/01 04:33:37]

If possible, let's return const char* to make this a bit more efficient.

[bashi, 2016/11/01 05:02:16]

Done.

+
 // This is an interface for components which can respond to memory status
 // changes. An initial state is NORMAL. See MemoryCoordinatorClientRegistry for
 // threading guarantees and ownership management.