Gardening: Update to latest revision.

Effecting CL: https://codereview.chromium.org/140593002
Events: Use EventConverterOzoneWayland to notify native output events.

We use EventConverterOzoneWayland to notify all native events coming from
Wayland to Aura. Output related events violate this and are sent directly to
OzoneDisplay. With this CL, we use EventConverterOzoneWayland to notify output
related events too. This change unifies the way native events are handled,
dispatched to various observers and removes un-necessary friend class
declaration in OzoneDisplay.
OzoneDisplay: Make OzoneProcessObserver inherit DestructionObserver.

Currently, OzoneDisplay inherits MessageLoop::DestructionObserver and informs
OzoneProcessObserver whenever MessageLoop is destroyed. This CL, changes it
so that OzoneProcessObserver inherits MessageLoop::DestructionObserver and gets
notified directly instead of OzoneDisplay having to do this.
OzoneDisplay: Remove SetWindowChangeObserver API.

WindowTreeHostDelegateWayland registers itself as WindowChangeObserver via
OzoneDisplay. This seems un-necessary as WindowTreeHostDelegateWayland can
do this directly via EventConverterOzoneWayland. This CL makes necessary
changes for this.

Fixes #186
OzoneDisplay: Move Window constants to a separate header.

WindowState and type are defined in OzoneDisplay. Moving these to a separate
header helps in explicitly defining the WindowType and state in IPC Messages.
This CL makes changes in this direction.
DRWH: Introduce interface for handling window state change events.

EventConverter handles native events coming from Wayland and dispatches them to
Aura. We need something similar to handle the case where Aura needs to send
native events(i.e. Creating Window, changing it's state etc) to Wayland. We
already have the code which does this but needs some re-arrangement. This CL
introduces WindowStateChangeHandler interface. The actual implementations will
be done in follow up CL.
WaylandDisplay and ODChannelHost to inherit WindowStateChangeHandler.

WindowState notifications need to be sent over IPC in multi process case and
handled in-process in single process case. OzoneDisplayChannelHost implements
WindowStateChangeHandler interface and sends any window state change
notifications over IPC (as it does now). WaylandDisplay implements
WindowStateChangeHandle interface and adds necessary support to handle the
events in GPU (multi-process case) or in Browser process (single-process case).
Take WindowStateChangeHandler into use.

This CL replaces the usage of OzoneDisplay SetWidget* APIS with the ones
introduced by WindowStateChangeHandler.
WindowStateChangeHandler: Remove all unused API in OzoneDisplay.

This CL removes all unused API in OzoneDisplay and DisplayChannelHost. All
these API have been replaced by WindowStateChangeHandler interface.
Style: Fix indentation.