Make Interaction Media Features MQ dynamic on Windows.

ui/events/devices/input_device_observer_win.cc

+// Copyright (c) 2017 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 "ui/events/devices/input_device_observer_win.h"
+
+#include "base/bind.h"
+#include "base/callback.h"
+#include "base/memory/singleton.h"
+#include "base/strings/string16.h"
+
+// This macro provides the implementation for the observer notification methods.
+#define NOTIFY_OBSERVERS(method_decl, observer_call)       \
+  void InputDeviceObserverWin::method_decl {               \
+    for (InputDeviceEventObserver & observer : observers_) \
+      observer.observer_call;                              \
+  }
+
+namespace ui {
+
+namespace {
+
+// The registry subkey that contains information about the state of the
+// detachable/convertible laptop, it tells if the device has an accessible
+// keyboard.
+// OEMs are expected to follow this guidelines to report docked/undocked state
+// https://msdn.microsoft.com/en-us/library/windows/hardware/dn922653(v=vs.85).aspx.

[mustaq, 2017/03/22 18:10:02]

I couldn't find a connection between ConvertibleSlateMode & this particular
registry key, so we need more info about how these two are related. Web search
for "PriorityControl" key suggests it's about process priority/scheduling which
vaguely matches the key's name.

Looks like "ConvertibleSlateMode" is only a part of the settings covered by this
key, right? Then we are definitely throwing redundant notifications here, which
could be bad for Chrome's run-time behavior. Do we have a way to "read" the
ConvertibleSlateMode value through this (or any other) registry key? We can then
cache the mode state here in this class, and fire notifications (from within
OnRegistryKeyChanged callback) only when the value changes.

In any case, we need to make sure that we don't have too frequent notifications.
Any Windows doc on which settings are covered by this key?

+const base::char16 kRegistryPriorityControl[] =
+    L"System\\CurrentControlSet\\Control\\PriorityControl";
+
+}  // namespace
+
+InputDeviceObserverWin::InputDeviceObserverWin() : weak_factory_(this) {
+  registry_key_.reset(new base::win::RegKey(
+      HKEY_LOCAL_MACHINE, kRegistryPriorityControl, KEY_NOTIFY | KEY_READ));
+
+  if (registry_key_->Valid()) {
+    // Start watching the registry for changes.
+    base::win::RegKey::ChangeCallback callback =
+        base::Bind(&InputDeviceObserverWin::OnRegistryKeyChanged,
+                   weak_factory_.GetWeakPtr(), registry_key_.get());
+    registry_key_->StartWatching(callback);
+  }
+}
+
+InputDeviceObserverWin* InputDeviceObserverWin::GetInstance() {
+  return base::Singleton<
+      InputDeviceObserverWin,
+      base::LeakySingletonTraits<InputDeviceObserverWin>>::get();
+}
+
+InputDeviceObserverWin::~InputDeviceObserverWin() {}
+
+void InputDeviceObserverWin::OnRegistryKeyChanged(base::win::RegKey* key) {
+  if (!key)
+    return;
+
+  // |OnRegistryKeyChanged| is removed as an observer when the ChangeCallback is
+  // called, so we need to re-register.
+  key->StartWatching(base::Bind(&InputDeviceObserverWin::OnRegistryKeyChanged,
+                                base::Unretained(this), base::Unretained(key)));
+
+  NotifyObserversTouchpadDeviceConfigurationChanged();
+  NotifyObserversMouseDeviceConfigurationChanged();
+  NotifyObserversKeyboardDeviceConfigurationChanged();
+}
+
+void InputDeviceObserverWin::AddObserver(InputDeviceEventObserver* observer) {
+  observers_.AddObserver(observer);
+}
+
+void InputDeviceObserverWin::RemoveObserver(
+    InputDeviceEventObserver* observer) {
+  observers_.RemoveObserver(observer);
+}
+
+NOTIFY_OBSERVERS(NotifyObserversKeyboardDeviceConfigurationChanged(),
+                 OnKeyboardDeviceConfigurationChanged());
+
+NOTIFY_OBSERVERS(NotifyObserversMouseDeviceConfigurationChanged(),
+                 OnMouseDeviceConfigurationChanged());
+
+NOTIFY_OBSERVERS(NotifyObserversTouchpadDeviceConfigurationChanged(),
+                 OnTouchpadDeviceConfigurationChanged());
+
+}  // namespace ui