Enable startup tracing from command line flags in components/tracing

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 61d1dd085da9c0d027516a5f68b63b4269bf5df4..7579285f84a44da64ad40c115172ec292c0b5c89 100644
--- a/base/trace_event/memory_dump_manager.h
+++ b/base/trace_event/memory_dump_manager.h
@@ -117,6 +117,9 @@ class BASE_EXPORT MemoryDumpManager : public TraceLog::EnabledStateObserver {
   void OnTraceLogEnabled() override;
   void OnTraceLogDisabled() override;
 
+  // Enable heap profiling if kEnableHeapProfiling is specified.
+  void EnableHeapProfilingIfNeeded();

[oystein (OOO til 10th of July), 2017/02/14 19:42:10]

Does this still need to be called from the MemoryDumpManager() constructor, in
addition to from the startup tracing? If not, it'd be nice to simplify it a bit
to just pass in the profiling_mode string.

[ssid, 2017/02/14 19:58:54]

Some processes may not enable startup tracing from content main runner. For
example, Renderer processes in Android do not use enable tracing in library
loader. So, for these cases we need to call this both from constructor and from
Initialize in case the constructor does not have command line initialized.

If the api becomes
EnableHeapProfiling(std::string flag_args);
Then all the call sites should read the flags :(

+
   // Returns true if the dump mode is allowed for current tracing session.
   bool IsDumpModeAllowed(MemoryDumpLevelOfDetail dump_mode);
 
@@ -309,9 +312,6 @@ class BASE_EXPORT MemoryDumpManager : public TraceLog::EnabledStateObserver {
   static void FinalizeDumpAndAddToTrace(
       std::unique_ptr<ProcessMemoryDumpAsyncState> pmd_async_state);
 
-  // Enable heap profiling if kEnableHeapProfiling is specified.
-  void EnableHeapProfilingIfNeeded();
-
   // Internal, used only by MemoryDumpManagerDelegate.
   // Creates a memory dump for the current process and appends it to the trace.
   // |callback| will be invoked asynchronously upon completion on the same