+cc bajones@ since he's the go-to spec guy.

v1.2 of the spec is making big changes, so this might not be relevant?

This was actually recently stripped out of the spec because it wasn't agreed upon what exactly it should represent. We should probably remove it from Blink's IDLs as well.

A possible patch is here : https://codereview.chromium.org/2736593002/;
Since the spec was updated, I'd like to update the API to the latest spec.

Let's get this in for M59.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/f4b1ca9d2d930fad5daaf6291a7a41c2eb141465

commit f4b1ca9d2d930fad5daaf6291a7a41c2eb141465
Author: shaobo.yan <shaobo.yan@intel.com>
Date: Thu Mar 09 01:13:32 2017

Update API to latest spec : Remove VRFrameData#timestamp
According to latest WebVR Spec, there are several changes. Remove VRFrameData#timestamp is one of them.

BUG= 697167 

Review-Url: https://codereview.chromium.org/2736593002
Cr-Commit-Position: refs/heads/master@{#455619}

[modify] https://crrev.com/f4b1ca9d2d930fad5daaf6291a7a41c2eb141465/chrome/browser/android/vr_shell/vr_shell.cc
[modify] https://crrev.com/f4b1ca9d2d930fad5daaf6291a7a41c2eb141465/device/vr/vr_service.mojom
[modify] https://crrev.com/f4b1ca9d2d930fad5daaf6291a7a41c2eb141465/third_party/WebKit/LayoutTests/external/wpt/webvr/idlharness-expected.txt
[modify] https://crrev.com/f4b1ca9d2d930fad5daaf6291a7a41c2eb141465/third_party/WebKit/LayoutTests/external/wpt/webvr/idlharness.html
[modify] https://crrev.com/f4b1ca9d2d930fad5daaf6291a7a41c2eb141465/third_party/WebKit/LayoutTests/vr/getFrameData_samewithinframe.html
[delete] https://crrev.com/10253f303a50e68dd30f5b1f372d30646366cc2e/third_party/WebKit/LayoutTests/vr/getFrameData_timestamp_updates.html
[modify] https://crrev.com/f4b1ca9d2d930fad5daaf6291a7a41c2eb141465/third_party/WebKit/LayoutTests/vr/resources/mock-vr-service.js
[modify] https://crrev.com/f4b1ca9d2d930fad5daaf6291a7a41c2eb141465/third_party/WebKit/LayoutTests/webexposed/global-interface-listing-expected.txt
[modify] https://crrev.com/f4b1ca9d2d930fad5daaf6291a7a41c2eb141465/third_party/WebKit/Source/modules/vr/VRFrameData.cpp
[modify] https://crrev.com/f4b1ca9d2d930fad5daaf6291a7a41c2eb141465/third_party/WebKit/Source/modules/vr/VRFrameData.h
[modify] https://crrev.com/f4b1ca9d2d930fad5daaf6291a7a41c2eb141465/third_party/WebKit/Source/modules/vr/VRFrameData.idl