Adds the UserInputMonitor implementation for Mac.

media/base/keyboard_event_counter.cc

Index: media/base/keyboard_event_counter.cc
diff --git a/media/base/keyboard_event_counter.cc b/media/base/keyboard_event_counter.cc
new file mode 100644
index 0000000000000000000000000000000000000000..0e78e014b7e7370467b1f709d8af9e893e558fa9
--- /dev/null
+++ b/media/base/keyboard_event_counter.cc
@@ -0,0 +1,42 @@
+// Copyright 2013 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 "media/base/keyboard_event_counter.h"
+
+#include "base/logging.h"
+
+namespace media {
+
+KeyboardEventCounter::KeyboardEventCounter() : total_key_presses_(0) {}
+
+KeyboardEventCounter::~KeyboardEventCounter() {}
+
+void KeyboardEventCounter::Reset() {
+  base::AutoLock auto_lock(lock_);
+  pressed_keys_.clear();
+  total_key_presses_ = 0;
+}
+
+void KeyboardEventCounter::OnKeyboardEvent(
+    ui::EventType event, ui::KeyboardCode key_code) {
+  base::AutoLock auto_lock(lock_);
+  // Updates the pressed keys and the total count of key presses.
+  if (event == ui::ET_KEY_PRESSED) {
+    if (pressed_keys_.find(key_code) != pressed_keys_.end())
+      return;
+    pressed_keys_.insert(key_code);
+    ++total_key_presses_;
+  } else {
+    DCHECK_EQ(ui::ET_KEY_RELEASED, event);
+    DCHECK(pressed_keys_.find(key_code) != pressed_keys_.end());

[Mark Mentovai, 2013/08/23 20:18:11]

There’s no possible way you can guarantee this condition unless you also have a
way to guarantee that no keys will be down when this object is constructed or
when Reset is called.

[jiayl, 2013/08/23 23:47:58]

removed.

+    pressed_keys_.erase(key_code);
+  }
+}
+
+size_t KeyboardEventCounter::GetKeyPressCount() const {
+  base::AutoLock auto_lock(lock_);

[Mark Mentovai, 2013/08/23 20:18:11]

This probably isn’t a hot spot, but you could make lock_ protect only
pressed_keys_, and use AtomicIncrement (base/atomicops.h) to manage
total_key_presses_. That would allow you to avoid taking the lock here.

[jiayl, 2013/08/23 23:47:58]

But the documentation in atomicops.h says that those routines should not be used
without solid evidence on performance improvement...so I didn't change here

[Mark Mentovai, 2013/08/26 15:11:01]

jiayl wrote:
Well, how often will GetKeyPressCount be called? It’s called from
AudioInputController::OnData, which seems like it might be called relatively
frequently. Removing a lock could be beneficial.

[jiayl, 2013/08/26 17:16:58]

But *_AtomicIncrement does not have a version for unsigned int.

[Mark Mentovai, 2013/08/26 19:07:55]

jiayl wrote:
A cast would be fine, although you’d need to pick the right type to cast to for
a size_t: it’d be Atomic32 in 32-bit builds and Atomic64 in 64-bit builds.

[jiayl, 2013/08/26 19:30:08]

Done.

+  return total_key_presses_;
+}
+
+}  // namespace media