I think this ought to be blocked on shipping the constructors. If it's shipped everywhere, which seems to be the case, I think we should also default to standardizing instead of removing, but is there something extra icky about there init*Event() methods?

Use counters:
https://www.chromestatus.com/metrics/feature/timeline/popularity/865
https://www.chromestatus.com/metrics/feature/timeline/popularity/866

That very low usage makes it not unthinkable to remove even though we have interop, but some upside to it would be nice.

Clarifying the usage a bit I've found a couple things by searching HTTP Archive which reference these functions:

 * TypeScript has annotations for these functions. Removal will have no effect.
 * Opal (Ruby-to-Javascript transpiler) has bindings for these functions but will attempt to use the constructor first.
 * VR View used to use these functions to generate synthetic DeviceMotionEvents but this code was removed.

Adding the constructor launch bug as a blocker.

I'm not sure if this counts as Firefox signaling deprecation but MDN lists initEvent() as deprecated:

https://developer.mozilla.org/en-US/docs/Web/API/Event/initEvent

It does not document these methods at all.

foolip@ suggests taking this a bit more slowly so I'm going to change this to a deprecation.

We've missed the M-58 branch point so retargeting for M-59.

reillyg@, is there no Blink>Foo component that covers this? Of the blocking bugs on issue 674593, this is the only one where I don't know which component to pick. (Doesn't matter since you're working on it, just seems odd.)

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/0921e8319f228e406019b434701ac9f181ee8ea1

commit 0921e8319f228e406019b434701ac9f181ee8ea1
Author: reillyg <reillyg@chromium.org>
Date: Fri Mar 17 19:27:01 2017

Remove non-standard DeviceOrientation Event initializers.

This patch removes DeviceOrientationEvent.initDeviceOrientationEvent
and DeviceMotionEvent.initDeviceMotionEvent and rewrites the LayoutTests
to use the constructors for these objects instead.

https://www.w3.org/TR/2016/CR-orientation-event-20160818/

BUG= 697598 

Review-Url: https://codereview.chromium.org/2728963004
Cr-Commit-Position: refs/heads/master@{#457849}

[modify] https://crrev.com/0921e8319f228e406019b434701ac9f181ee8ea1/android_webview/tools/system_webview_shell/test/data/webexposed/global-interface-listing-expected.txt
[modify] https://crrev.com/0921e8319f228e406019b434701ac9f181ee8ea1/third_party/WebKit/LayoutTests/device_orientation/motion/optional-event-properties-expected.txt
[modify] https://crrev.com/0921e8319f228e406019b434701ac9f181ee8ea1/third_party/WebKit/LayoutTests/device_orientation/motion/optional-event-properties.html
[modify] https://crrev.com/0921e8319f228e406019b434701ac9f181ee8ea1/third_party/WebKit/LayoutTests/device_orientation/orientation/optional-event-properties-expected.txt
[modify] https://crrev.com/0921e8319f228e406019b434701ac9f181ee8ea1/third_party/WebKit/LayoutTests/device_orientation/orientation/optional-event-properties.html
[modify] https://crrev.com/0921e8319f228e406019b434701ac9f181ee8ea1/third_party/WebKit/LayoutTests/platform/mac/virtual/stable/webexposed/global-interface-listing-expected.txt
[modify] https://crrev.com/0921e8319f228e406019b434701ac9f181ee8ea1/third_party/WebKit/LayoutTests/platform/win/virtual/stable/webexposed/global-interface-listing-expected.txt
[modify] https://crrev.com/0921e8319f228e406019b434701ac9f181ee8ea1/third_party/WebKit/LayoutTests/webexposed/global-interface-listing-expected.txt
[delete] https://crrev.com/6f7dd6b21b0aa119cc9415a1b714bb106646a066/third_party/WebKit/Source/bindings/modules/v8/custom/V8DeviceMotionEventCustom.cpp
[modify] https://crrev.com/0921e8319f228e406019b434701ac9f181ee8ea1/third_party/WebKit/Source/bindings/modules/v8/custom/custom.gni
[modify] https://crrev.com/0921e8319f228e406019b434701ac9f181ee8ea1/third_party/WebKit/Source/modules/device_orientation/DeviceMotionEvent.cpp
[modify] https://crrev.com/0921e8319f228e406019b434701ac9f181ee8ea1/third_party/WebKit/Source/modules/device_orientation/DeviceMotionEvent.h
[modify] https://crrev.com/0921e8319f228e406019b434701ac9f181ee8ea1/third_party/WebKit/Source/modules/device_orientation/DeviceMotionEvent.idl
[modify] https://crrev.com/0921e8319f228e406019b434701ac9f181ee8ea1/third_party/WebKit/Source/modules/device_orientation/DeviceOrientationEvent.cpp
[modify] https://crrev.com/0921e8319f228e406019b434701ac9f181ee8ea1/third_party/WebKit/Source/modules/device_orientation/DeviceOrientationEvent.h
[modify] https://crrev.com/0921e8319f228e406019b434701ac9f181ee8ea1/third_party/WebKit/Source/modules/device_orientation/DeviceOrientationEvent.idl

Marking launch approved per LGTMs on the blink-dev Intent to Deprecate and Remove thread:

https://groups.google.com/a/chromium.org/d/msg/blink-dev/XlnBk6qzkuw/u5TZshloEAAJ