Adds the UserInputMonitor implementation for Mac.

media/base/user_input_monitor.h

Index: media/base/user_input_monitor.h
diff --git a/media/base/user_input_monitor.h b/media/base/user_input_monitor.h
index 9eb82f334f833612a0720367c83c4513ba275bef..e58d7b268700ec6ad80d28f8ffae512939f56245 100644
--- a/media/base/user_input_monitor.h
+++ b/media/base/user_input_monitor.h
@@ -9,7 +9,6 @@
 
 #include "base/memory/ref_counted.h"
 #include "base/memory/scoped_ptr.h"
-#include "base/memory/weak_ptr.h"
 #include "base/observer_list.h"
 #include "base/synchronization/lock.h"
 #include "media/base/media_export.h"
@@ -28,6 +27,8 @@ namespace media {
 // Thread safe. The thread on which the listenters are called is not guaranteed.
 // The callers should not perform expensive/blocking tasks in the callback since
 // it might be called on the browser UI/IO threads.
+// The object must outlive the browser UI/IO threads to make sure the callbacks
+// will not access deleted object.
 class MEDIA_EXPORT UserInputMonitor {
  public:
   // The interface to receive mouse movement events.
@@ -39,17 +40,6 @@ class MEDIA_EXPORT UserInputMonitor {
    protected:
     virtual ~MouseEventListener() {}
   };
-  // The interface to receive key stroke events.
-  class MEDIA_EXPORT KeyStrokeListener {
-   public:
-    // Called when any key is pressed. Called only once until the key is
-    // released, i.e. holding down a key for a long period will generate one
-    // callback just when the key is pressed down.
-    virtual void OnKeyStroke() = 0;
-
-   protected:
-    virtual ~KeyStrokeListener() {}
-  };
 
   virtual ~UserInputMonitor();
 
@@ -65,8 +55,15 @@ class MEDIA_EXPORT UserInputMonitor {
   // destroyed.
   void AddMouseListener(MouseEventListener* listener);
   void RemoveMouseListener(MouseEventListener* listener);
-  void AddKeyStrokeListener(KeyStrokeListener* listener);
-  void RemoveKeyStrokeListener(KeyStrokeListener* listener);
+
+  // The callers must call EnableKeyPressMonitoring before calling

[Mark Mentovai, 2013/08/23 18:09:03]

“A caller must call”

That clarifies that it’s OK for more than one caller to call Enable.

+  // GetKeyPressCount(), and call DisableKeyPressMonitoring when it no
+  // longer needs it.
+  void EnableKeyPressMonitoring();
+  void DisableKeyPressMonitoring();
+  // Returns the number of Key presses since the first KeyPressCounterReference

[Mark Mentovai, 2013/08/23 18:09:03]

Let’s get a blank line before this, because otherwise it sort of bleeds into the
declarations that come before it.

[Mark Mentovai, 2013/08/23 18:09:03]

Key is not a proper noun, it shouldn’t be capitalized.

Actually, “keypresses” is fine as a single compound word.

[Mark Mentovai, 2013/08/23 18:09:03]

This comment introduces the concept of a KeyPressCounterReference but doesn’t
explain it, and that word isn’t found anywhere else in this file. Revise the
comment. It should probably say something about the first
EnableKeyPressMonitoring instead.

+  // is added. Auto-repeated key presses are not counted.

[Mark Mentovai, 2013/08/23 18:09:03]

It’s fine if the implementation doesn’t count auto-repeated keypresses, but I
don’t think that this is a very important feature of GetKeyPressCount, and I
don’t think that it should be mentioned here. It’d be totally fine, I think, if
an implementation did count auto-repeated keypresses.

This is the sort of thing that you can mention at the actual implementation
site.

+  virtual size_t GetKeyPressCount() const;
 
  protected:
   UserInputMonitor();
@@ -82,14 +79,14 @@ class MEDIA_EXPORT UserInputMonitor {
   virtual void StartKeyboardMonitoring() = 0;
   virtual void StopKeyboardMonitoring() = 0;
 
-  base::Lock lock_;
+  mutable base::Lock lock_;

[Mark Mentovai, 2013/08/23 18:09:03]

What sort of constness is changing that requires this now?

   ObserverList<MouseEventListener, true> mouse_listeners_;
-  ObserverList<KeyStrokeListener, true> key_stroke_listeners_;
   bool monitoring_mouse_;
-  bool monitoring_keyboard_;
+  size_t key_press_counter_references_;
   // The set of keys currently held down. Used for convering raw keyboard events
   // into KeyStrokeListener callbacks.
-  std::set<ui::KeyboardCode> pressed_keys_;
+  std::set<int> pressed_keys_;

[Mark Mentovai, 2013/08/23 18:09:03]

This is irrelevant on at least one platform now.

+  size_t total_key_presses_;
 
   DISALLOW_COPY_AND_ASSIGN(UserInputMonitor);
 };