[tracing] Add filtering mode in TraceLog

base/trace_event/memory_dump_manager.cc

Index: base/trace_event/memory_dump_manager.cc
diff --git a/base/trace_event/memory_dump_manager.cc b/base/trace_event/memory_dump_manager.cc
index 9719a6c672086ad9fc9f1c0d815c0b127efcb430..c095a81967edddfc7d3da82674cad74d02c00e98 100644
--- a/base/trace_event/memory_dump_manager.cc
+++ b/base/trace_event/memory_dump_manager.cc
@@ -201,12 +201,31 @@ void MemoryDumpManager::Initialize(MemoryDumpManagerDelegate* delegate,
                        nullptr);
 #endif
 
+  TRACE_EVENT_WARMUP_CATEGORY(kTraceCategory);
+
+  // TODO(ssid): This should be done in EnableHeapProfiling so that we capture
+  // more allocations (crbug.com/625170).
+  if (AllocationContextTracker::capture_mode() ==
+          AllocationContextTracker::CaptureMode::PSEUDO_STACK &&
+      !(TraceLog::GetInstance()->enabled_modes() & TraceLog::FILTERING_MODE)) {
+    TraceConfig::EventFilterConfig heap_profiler_filter_config(
+        TraceLog::TraceEventFilter::kHeapProfilerPredicate);
+    heap_profiler_filter_config.AddIncludedCategory("*");
+    heap_profiler_filter_config.AddIncludedCategory(
+        MemoryDumpManager::kTraceCategory);
+    TraceConfig::EventFilters filters;
+    filters.push_back(heap_profiler_filter_config);
+    TraceConfig filtering_trace_config;
+    filtering_trace_config.SetEventFilterConfigs(filters);
+    TraceLog::GetInstance()->SetEnabled(filtering_trace_config,

[oystein (OOO til 10th of July), 2016/10/13 00:34:29]

bikeshedding readability nit: Maybe a break here and a comment on top of the
above block that states this is just prepping the config, to make it immediately
obvious that's the main thing happening here.

// Configure the filtering TraceConfig
TraceConfig filtering_trace_config;
... do stuff to filtering_trace_config;

TraceLog::GetInstance()->SetEnabled(filtering_trace_config,
TraceLog::FILTERING_MODE);

[ssid, 2016/10/13 17:30:54]

Done.

+                                        TraceLog::FILTERING_MODE);
+  }
+
   // If tracing was enabled before initializing MemoryDumpManager, we missed the
   // OnTraceLogEnabled() event. Synthetize it so we can late-join the party.
-  bool is_tracing_already_enabled = TraceLog::GetInstance()->IsEnabled();
-  TRACE_EVENT0(kTraceCategory, "init");  // Add to trace-viewer category list.
+  bool tracing_already_enabled = TraceLog::GetInstance()->IsEnabled();

[oystein (OOO til 10th of July), 2016/10/13 00:34:29]

nit and not about this CL (but since you're touching it :): Why isn't the
IsEnabled() call just inlined in the if() two lines below? The current ordering
makes it seem like AddEnabledStateObserver() can have side-effects in terms of
enabling the TraceLog, which it can't. Or is this some threading thing? Deserves
a comment if so.

[ssid, 2016/10/13 17:30:54]

Um, this is done here so that we do not call OnTraceLogEnabled twice.
There could be a case where:
thread 1: AddObserver
thread 1: IsEnabled -> false
thread 2: SetEnabled and observer->OnTraceLogEnabled
thread 1: OnTraceLogEnabled // since the previous IsEnabled returned false.

This could cause double initialization of the dump timer which is worse than in
few cases here which will not enable timer at all.

[Primiano Tucci (use gerrit), 2016/10/13 19:11:24]

Correct ;-)

[oystein (OOO til 10th of July), 2016/10/13 19:20:18]

Yep makes sense; comment still needed I think :)

   TraceLog::GetInstance()->AddEnabledStateObserver(this);
-  if (is_tracing_already_enabled)
+  if (tracing_already_enabled)
     OnTraceLogEnabled();
 }