Adds the UserInputMonitor implementation for Mac.

media/audio/audio_input_controller.cc

Index: media/audio/audio_input_controller.cc
diff --git a/media/audio/audio_input_controller.cc b/media/audio/audio_input_controller.cc
index f7747b9d37fb77b948b34e0daf2e3a8407905f56..98461b0250a5d5d1cdd73b1d110fe579ec00316b 100644
--- a/media/audio/audio_input_controller.cc
+++ b/media/audio/audio_input_controller.cc
@@ -9,6 +9,10 @@
 #include "media/base/limits.h"
 #include "media/base/scoped_histogram_timer.h"
 
+#if defined(OS_MACOSX)
+#include <ApplicationServices/ApplicationServices.h>
+#endif
+
 namespace {
 const int kMaxInputChannels = 2;
 
@@ -46,6 +50,7 @@ AudioInputController::AudioInputController(EventHandler* handler,
       sync_writer_(sync_writer),
       max_volume_(0.0),
       user_input_monitor_(user_input_monitor),
+      prev_key_down_count_(0),
       key_pressed_(false) {
   DCHECK(creator_loop_.get());
 }
@@ -334,6 +339,14 @@ void AudioInputController::OnData(AudioInputStream* stream, const uint8* data,
                                   uint32 size, uint32 hardware_delay_bytes,
                                   double volume) {
   bool key_pressed = false;
+#if defined(OS_MACOSX)
+  uint32_t current_count = CGEventSourceCounterForEventType(

[Mark Mentovai, 2013/08/22 18:27:52]

I don’t know much about when this thing is called. Is it guaranteed to be called
frequently? Or does it ever “pause?”

If it pauses, then when “unpaused,” you’ll need to reset prev_key_down_count_ to
the current counter value, otherwise it’ll give a false positive if any key had
been pressed during the paused interval.

In any case, if there isn’t a very long pause between the time an object of this
class is constructed and when OnData starts being called, you should initialize
prev_key_down_count_ to the correct value in the constructor. Then you can
remove the != 0 check on line 345. If the constructor is inappropriate but there
is some “start” function, you can initialize prev_key_down_count_ there instead.

[jiayl, 2013/08/22 18:51:16]

Done initialization in DoRecord.
I don't think it ever pauses unless the device is removed.
Dale, could you confirm?

+      kCGEventSourceStateHIDSystemState, kCGEventKeyDown);
+  if (current_count > prev_key_down_count_ && prev_key_down_count_ != 0) {

[Mark Mentovai, 2013/08/22 18:27:52]

If you change > to !=, then this handles rollover (counter overflow) too.

[jiayl, 2013/08/22 18:51:16]

Done.

+    key_pressed = true;
+  }
+  prev_key_down_count_ = current_count;
+#else
   {
     base::AutoLock auto_lock(lock_);
     if (state_ != kRecording)
@@ -341,6 +354,7 @@ void AudioInputController::OnData(AudioInputStream* stream, const uint8* data,
 
     std::swap(key_pressed, key_pressed_);
   }
+#endif  // defined(OS_MACOSX)
 
   // Mark data as active to ensure that the periodic calls to
   // DoCheckForNoData() does not report an error to the event handler.