Makes the BattOrAgent asynchronous

tools/battor_agent/battor_agent_bin.cc

Index: tools/battor_agent/battor_agent_bin.cc
diff --git a/tools/battor_agent/battor_agent_bin.cc b/tools/battor_agent/battor_agent_bin.cc
index 5980403dbb8dd93321bf0fb2b8ae10e671aed9e4..9caa3bd32c86285440dfc6bd9c192199e61e50e9 100644
--- a/tools/battor_agent/battor_agent_bin.cc
+++ b/tools/battor_agent/battor_agent_bin.cc
@@ -2,8 +2,16 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+// This file provides a thin binary wrapper around the BattOr Agent
+// library. This binary wrapper provides a means for non-C++ tracing
+// controllers, such as Telemetry and Android Systrace, to issue high-level
+// tracing commands to the BattOr..
+
 #include <iostream>
 
+#include "base/bind.h"
+#include "base/memory/scoped_ptr.h"
+#include "base/synchronization/waitable_event.h"
 #include "tools/battor_agent/battor_agent.h"
 
 using std::cout;
@@ -12,12 +20,16 @@ using std::string;
 
 namespace {
 
+// An event used to signal that the BattOr Agent has finished executing its
+// command.
+base::WaitableEvent g_stop_tracing_complete_event(false, false);
+
 void PrintUsage() {
   cout << "Usage: battor_agent <command> <arguments>" << endl << endl
        << "Commands:" << endl << endl
        << "  StartTracing <path>" << endl
        << "  StopTracing <path>" << endl
-       << "  SupportsExplicitClockSync <path>" << endl
+       << "  SupportsExplicitClockSync" << endl
        << "  RecordClockSyncMarker <path> <marker>" << endl
        << "  IssueClockSyncMarker <path>" << endl
        << "  Help" << endl;
@@ -36,6 +48,10 @@ bool GetArg(int argnum, int argc, char* argv[], string* value) {
   return true;
 }
 
+void OnCommandComplete() {
+  g_stop_tracing_complete_event.Signal();
+}
+
 } // namespace
 
 int main(int argc, char* argv[]) {
@@ -55,10 +71,12 @@ int main(int argc, char* argv[]) {
     if (!GetArg(2, argc, argv, &path))
       return 1;
 
-    string out_trace;
     cout << "Calling StopTracing()" << endl;
-    battor::BattOrAgent(path).StopTracing(&out_trace);
-    cout << out_trace << endl;
+    std::string trace_output;
+    battor::BattOrAgent(path)
+        .StopTracing(&trace_output, base::Bind(&OnCommandComplete));
+    g_stop_tracing_complete_event.Wait();
+    cout << trace_output << endl;
   } else if (cmd == "SupportsExplicitClockSync") {
     cout << "Calling SupportsExplicitClockSync" << endl;
     cout << battor::BattOrAgent::SupportsExplicitClockSync() << endl;
@@ -69,7 +87,11 @@ int main(int argc, char* argv[]) {
 
     cout << "Marker: " << marker << endl;
     cout << "Calling RecordClockSyncMarker()" << endl;
-    battor::BattOrAgent(path).RecordClockSyncMarker(marker);
+    // TODO(charliea): Write the  time to STDOUT
+    battor::BattOrAgent(path)
+        .RecordClockSyncMarker(marker, base::Bind(&OnCommandComplete));
+    g_stop_tracing_complete_event.Wait();
+    // TODO(charliea): Write the time to STDOUT
   } else if (cmd == "IssueClockSyncMarker") {
     string path;
     if (!GetArg(2, argc, argv, &path))