[memory-infra] Add support for polling memory totals in MemoryDumpManager

base/trace_event/memory_dump_manager.h

Index: base/trace_event/memory_dump_manager.h
diff --git a/base/trace_event/memory_dump_manager.h b/base/trace_event/memory_dump_manager.h
index 06b772c6e4bd5f050ee6079ba6aacf1b987dfb19..40a45943ff6a96f2a07dee675996408ce242341f 100644
--- a/base/trace_event/memory_dump_manager.h
+++ b/base/trace_event/memory_dump_manager.h
@@ -94,7 +94,8 @@ class BASE_EXPORT MemoryDumpManager : public TraceLog::EnabledStateObserver {
   // This method takes ownership of the dump provider and guarantees that:
   //  - The |mdp| will be deleted at some point in the near future.
   //  - Its deletion will not happen concurrently with the OnMemoryDump() call.
-  // Note that OnMemoryDump() calls can still happen after this method returns.
+  // Note that OnMemoryDump() and PollFastMemoryTotal() calls can still happen
+  // after this method returns.
   void UnregisterAndDeleteDumpProviderSoon(
       std::unique_ptr<MemoryDumpProvider> mdp);
 
@@ -329,6 +330,12 @@ class BASE_EXPORT MemoryDumpManager : public TraceLog::EnabledStateObserver {
   // runner.
   void InvokeOnMemoryDump(ProcessMemoryDumpAsyncState* owned_pmd_async_state);
 
+  // Records a quick total memory usage value that can be polled in short

[Primiano Tucci (use gerrit), 2016/12/15 16:45:01]

"that can be polled in short intervals" is quite redundant. the "quick" part
above should be enough.

[ssid, 2016/12/16 02:31:54]

Done.

+  // intervals. This is used to track the memory usage of process without having
+  // to record all data from dump providers and for detecting peak usages.
+  // Must be called on the dump thread task runner.
+  void PollFastMemoryTotal(uint64_t* memory_total);

[Primiano Tucci (use gerrit), 2016/12/15 16:45:01]

I'd probably add also: this value is approximate to trade-off speed, and not
consistent with the rest of the memory-infra metrics.

[ssid, 2016/12/16 02:31:54]

Done.

+
   // Helper for RegierDumpProvider* functions.
   void RegisterDumpProviderInternal(
       MemoryDumpProvider* mdp,
@@ -340,6 +347,14 @@ class BASE_EXPORT MemoryDumpManager : public TraceLog::EnabledStateObserver {
   void UnregisterDumpProviderInternal(MemoryDumpProvider* mdp,
                                       bool take_mdp_ownership_and_delete_async);
 
+  // Adds / removes polling supported provider to the copy

[Primiano Tucci (use gerrit), 2016/12/15 16:45:01]

s/polling supported provider/providers that support fast polling/
also remove the "copy". I know what you meant there but IMHO is more confusing
than explanatory.

[ssid, 2016/12/16 02:31:54]

Done.

+  // |mdps_for_fast_polling_|. This function should run on the dump thread so

[Primiano Tucci (use gerrit), 2016/12/15 16:45:01]

No need for the "This function should run..." part. "OnDumpThread" as part of
the name should be pretty clear ;-)

[ssid, 2016/12/16 02:31:54]

Done.

+  // that we don't need lock for polling.
+  void RegisterPollingMDPOnDumpThread(
+      scoped_refptr<MemoryDumpProviderInfo> mdpinfo);
+  void UnregisterPollingMDPOnDumpThread(
+      scoped_refptr<MemoryDumpProviderInfo> mdpinfo);
+
   // An ordererd set of registered MemoryDumpProviderInfo(s), sorted by task
   // runner affinity (MDPs belonging to the same task runners are adjacent).
   MemoryDumpProviderInfo::OrderedSet dump_providers_;
@@ -349,6 +364,10 @@ class BASE_EXPORT MemoryDumpManager : public TraceLog::EnabledStateObserver {
 
   MemoryDumpManagerDelegate* delegate_;  // Not owned.
 
+  // A copy of mdpinfo list that support polling. It must be accessed only on
+  // the dump thread for polling without taking lock.
+  MemoryDumpProviderInfo::OrderedSet mdps_for_fast_polling_;

[Primiano Tucci (use gerrit), 2016/12/15 16:45:01]

for readability and consistency I would:
move this just after dump_providers_
call it dumps_providers_for_polling_ 

[ssid, 2016/12/16 02:31:54]

Done.

+
   // When true, this instance is in charge of coordinating periodic dumps.
   bool is_coordinator_;