Fix Volume slider is captured in screenshot done in touchview mode

ash/common/system/tray/system_tray_notifier.h

Index: ash/common/system/tray/system_tray_notifier.h
diff --git a/ash/common/system/tray/system_tray_notifier.h b/ash/common/system/tray/system_tray_notifier.h
index 29bb9f521061c39977d5f613cee9636c32ef3d10..a1917bd586d79c4083d79d9321df1853030142a7 100644
--- a/ash/common/system/tray/system_tray_notifier.h
+++ b/ash/common/system/tray/system_tray_notifier.h
@@ -24,6 +24,7 @@ class AccessibilityObserver;
 class AudioObserver;
 class ClockObserver;
 class IMEObserver;
+class MaximizeModeScreenshotObserver;
 struct UpdateInfo;
 class UpdateObserver;
 class UserObserver;
@@ -97,6 +98,13 @@ class ASH_EXPORT SystemTrayNotifier {
   void NotifyUserUpdate();
   void NotifyUserAddedToSession();
 
+  // Maximize mode screenshot.
+  void AddMaxModeScreenshotObserver(MaximizeModeScreenshotObserver* observer);

[Daniel Erat, 2016/07/27 23:51:31]

s/MaxMode/MaximizeMode/ here and on the next line; "MaxMode" doesn't look like
it's currently used anywhere in the code

[Qiang(Joe) Xu, 2016/07/28 03:27:18]

Done.

+  void RemoveMaxModeScreenshotObserver(
+      MaximizeModeScreenshotObserver* observer);
+  void NotifyWillTakeScreenshot(int volume_percent);
+  void NotifyDidTakeScreenshot();

[Daniel Erat, 2016/07/27 23:51:31]

maybe rename these to:

  NotifyWillTakeScreenshotInMaximizeMode
  NotifyDidTakeScreenshotInMaximizeMode

? the current names don't accurately reflect when they should be called. the
observer would need to be updated too.

actually, i'm wondering if the names should also explain that these are only
called for the volume-down+power accelerator in particular.

but it feels like this is so special-purpose that it's hard to justify an
observer interface. can PowerButtonController call directly into TrayAudio to
notify it about things, or is that a layering violation?

what about if TrayAudio had a SuppressNotification() method that PBC could call,
and then PBC handled saving the original volume and restoring it later all on
its own? that seems like it greatly cuts down the complexity of this change.

[Qiang(Joe) Xu, 2016/07/28 00:15:39]

Hi, to get a better understanding, what is SuppressNotification this paragraph
meaning? I cannot see a code example in code base. Thanks!

[Daniel Erat, 2016/07/28 00:25:56]

i meant that PBC could call a new TrayAudio method with a signature like:

  void SuppressNotification(bool suppress);

(or maybe HideNotification is clearer) when it wants to hide or unhide
notifications.

[Qiang(Joe) Xu, 2016/07/28 03:27:18]

I still keep MaximizeModeScreenshotObserver in SystemTrayNotifier for these
reasons.
1. I cannot figure out a way to call methods of TrayAudio from PBC.
2. |hide_popup_| needs to be set in TrayAudio and modifies
OnOutputNodeVolumeChanged method, which makes I believe it still needs the
observer.
3. I tried move the observer as a nested class in PBC, however
ash::Shell::GetInstance()->power_button_controller()->AddObserver in TrayAudio
breaks the DEPS rule. "ash/common" cannot includes "ash/".

For 1. SystemTray doesn't expose TrayAudio reference. Could I expose that?
https://cs.chromium.org/chromium/src/ash/common/system/tray/system_tray.h?q=s...
It only provides the accessors for testing purpose.

+
 #if defined(OS_CHROMEOS)
   // Bluetooth.
   void AddBluetoothObserver(BluetoothObserver* observer);
@@ -174,6 +182,8 @@ class ASH_EXPORT SystemTrayNotifier {
   base::ObserverList<ClockObserver> clock_observers_;
   base::ObserverList<IMEObserver> ime_observers_;
   base::ObserverList<LocaleObserver> locale_observers_;
+  base::ObserverList<MaximizeModeScreenshotObserver>
+      maximize_mode_screenshot_observers_;
   base::ObserverList<UpdateObserver> update_observers_;
   base::ObserverList<UserObserver> user_observers_;