Adding key press detection in the browser process.

media/audio/key_press_monitor.cc

+// Copyright (c) 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/audio/key_press_monitor.h"
+
+#include "base/message_loop/message_loop_proxy.h"
+
+namespace media {
+
+KeyPressMonitor::KeyPressMonitor(
+    const scoped_refptr<base::MessageLoopProxy>& message_loop,
+    const scoped_refptr<base::MessageLoopProxy>& io_message_loop,

[DaleCurtis, 2013/08/07 17:50:39]

Not really necessary to pass all this in, you could just use
BrowserThread::GetMessageLoopForThread().

[DaleCurtis, 2013/08/07 18:58:02]

I forgot this is in media/ so you can't do this after all.

+    const scoped_refptr<base::MessageLoopProxy>& ui_message_loop)
+    : message_loop_(message_loop),
+      io_message_loop_(io_message_loop),
+      ui_message_loop_(ui_message_loop),
+      weak_ptr_factory_(this) {}
+
+KeyPressMonitor::~KeyPressMonitor() {}
+
+void KeyPressMonitor::OnMouseMoved(const SkIPoint& position) {
+  NOTREACHED();
+}
+
+void KeyPressMonitor::OnKeyboardEvent(ui::EventType event,
+                                      ui::KeyboardCode key_code) {
+  DCHECK(message_loop_->BelongsToCurrentThread());
+  if (event == ui::ET_KEY_PRESSED) {
+    if (pressed_keys_.find(key_code) != pressed_keys_.end())
+      return;
+    pressed_keys_.insert(key_code);
+    FOR_EACH_OBSERVER(KeyPressListener, listeners_, OnKeyPressed());

[tommi (sloooow) - chröme, 2013/08/06 10:57:47]

Would it make sense to have two events, OnKeyPressed(key) and
OnKeyReleased(key), to keep track of whether or not a key is being pressed?  I
guess some sort of reference counting would need to be used, but that might
perhaps be closer to the behavior that the webrtc code used to do.

Actually... since you already have a map of pressed keys, what about having an
event to indicate that no keys are being pressed and use that to clear the
key_pressed_ flag?

[jiayl, 2013/08/06 17:24:11]

It doesn't seem necessary if my understanding of the existing webrtc impl is
correct (see my reply to the other comment). If you are concerned about the case
of holding down a key without releasing it, KeyPressMonitor already takes care
of that case and only notifies the listeners once. IMO the clients of
KeyPressMonitor don't need to know which keys are pressed or released; these
logic should be hidden in KeyPressMonitor. 

+  } else {
+    DCHECK(event == ui::ET_KEY_RELEASED);
+    DCHECK(pressed_keys_.find(key_code) != pressed_keys_.end());
+    pressed_keys_.erase(key_code);
+  }
+}
+
+void KeyPressMonitor::AddKeyPressListener(KeyPressListener* listener) {
+  DCHECK(message_loop_->BelongsToCurrentThread());
+  listeners_.AddObserver(listener);
+
+  if (listeners_.size() == 1 && !monitor_.get()) {
+    monitor_.reset(UserInputMonitor::Create(io_message_loop_,
+                                            ui_message_loop_,
+                                            message_loop_,
+                                            UserInputMonitor::KEYBOARD_EVENT,
+                                            weak_ptr_factory_.GetWeakPtr())
+                       .release());
+  }
+}
+
+void KeyPressMonitor::RemoveKeyPressListener(KeyPressListener* listener) {
+  DCHECK(message_loop_->BelongsToCurrentThread());
+  listeners_.RemoveObserver(listener);
+
+  if (listeners_.size() == 0) {
+    monitor_.reset(NULL);
+    weak_ptr_factory_.InvalidateWeakPtrs();
+  }
+}
+
+}  // namespace media