[Startup Tracing] Enable startup tracing from config file

content/app/android/library_loader_hooks.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "content/app/android/library_loader_hooks.h"
 
 #include "base/android/base_jni_registrar.h"
 #include "base/android/command_line_android.h"
 #include "base/android/jni_android.h"
 #include "base/android/jni_registrar.h"
@@ skipping 77 matching lines @@
 }
 
 bool LibraryLoaded(JNIEnv* env, jclass clazz) {
   base::CommandLine* command_line = base::CommandLine::ForCurrentProcess();
 
   if (command_line->HasSwitch(switches::kTraceStartup)) {
     base::trace_event::TraceConfig trace_config(
         command_line->GetSwitchValueASCII(switches::kTraceStartup), "");
     base::trace_event::TraceLog::GetInstance()->SetEnabled(
         trace_config, base::trace_event::TraceLog::RECORDING_MODE);
+  } else {
+    base::trace_event::EnableStartupTracingIfConfigFileExists();
   }
 
   // Android's main browser loop is custom so we set the browser
   // name here as early as possible.
   TRACE_EVENT_BEGIN_ETW("BrowserMain", 0, "");
   base::trace_event::TraceLog::GetInstance()->SetProcessName("Browser");
   base::trace_event::TraceLog::GetInstance()->SetProcessSortIndex(
       kTraceEventBrowserProcessSortIndex);
 
   // Can only use event tracing after setting up the command line.
   TRACE_EVENT0("jni", "JNI_OnLoad continuation");
 
   logging::LoggingSettings settings;
   settings.logging_dest = logging::LOG_TO_SYSTEM_DEBUG_LOG;
   logging::InitLogging(settings);
   // To view log output with IDs and timestamps use "adb logcat -v threadtime".
   logging::SetLogItems(false,    // Process ID
                        false,    // Thread ID
                        false,    // Timestamp
                        false);   // Tick count
   VLOG(0) << "Chromium logging enabled: level = " << logging::GetMinLogLevel()
           << ", default verbosity = " << logging::GetVlogVerbosity();
 
   return true;
 }
 
 }  // namespace content