The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/868006705aed11538a1402f4db46953e2cfe2a5a

commit 868006705aed11538a1402f4db46953e2cfe2a5a
Author: peter <peter@chromium.org>
Date: Thu May 18 18:43:15 2017

Implement and ship PushSubscription.expirationTime

This property tells developers the time after which the subscription
will be deactivated, if any. Since we don't support refreshing
subscriptions yet, it always returns NULL.

Specification:
https://w3c.github.io/push-api/#dom-pushsubscription-expirationtime

Intent to Implement and Ship:
https://groups.google.com/a/chromium.org/d/topic/blink-dev/xCTqjIDrOm4/discussion

BUG= 718837 

Review-Url: https://codereview.chromium.org/2864603003
Cr-Commit-Position: refs/heads/master@{#472886}

[modify] https://crrev.com/868006705aed11538a1402f4db46953e2cfe2a5a/third_party/WebKit/LayoutTests/http/tests/push_messaging/push-subscription-stringification.html
[modify] https://crrev.com/868006705aed11538a1402f4db46953e2cfe2a5a/third_party/WebKit/LayoutTests/http/tests/push_messaging/subscribe-success-in-document.html
[modify] https://crrev.com/868006705aed11538a1402f4db46953e2cfe2a5a/third_party/WebKit/LayoutTests/http/tests/serviceworker/webexposed/global-interface-listing-service-worker-expected.txt
[modify] https://crrev.com/868006705aed11538a1402f4db46953e2cfe2a5a/third_party/WebKit/LayoutTests/platform/mac/virtual/stable/http/tests/serviceworker/webexposed/global-interface-listing-service-worker-expected.txt
[modify] https://crrev.com/868006705aed11538a1402f4db46953e2cfe2a5a/third_party/WebKit/LayoutTests/platform/mac/virtual/stable/webexposed/global-interface-listing-dedicated-worker-expected.txt
[modify] https://crrev.com/868006705aed11538a1402f4db46953e2cfe2a5a/third_party/WebKit/LayoutTests/platform/mac/virtual/stable/webexposed/global-interface-listing-expected.txt
[modify] https://crrev.com/868006705aed11538a1402f4db46953e2cfe2a5a/third_party/WebKit/LayoutTests/platform/mac/virtual/stable/webexposed/global-interface-listing-shared-worker-expected.txt
[modify] https://crrev.com/868006705aed11538a1402f4db46953e2cfe2a5a/third_party/WebKit/LayoutTests/platform/win/virtual/stable/webexposed/global-interface-listing-expected.txt
[modify] https://crrev.com/868006705aed11538a1402f4db46953e2cfe2a5a/third_party/WebKit/LayoutTests/virtual/service-worker-navigation-preload-disabled/http/tests/serviceworker/webexposed/global-interface-listing-service-worker-expected.txt
[modify] https://crrev.com/868006705aed11538a1402f4db46953e2cfe2a5a/third_party/WebKit/LayoutTests/virtual/service-worker-navigation-preload-disabled/webexposed/global-interface-listing-dedicated-worker-expected.txt
[modify] https://crrev.com/868006705aed11538a1402f4db46953e2cfe2a5a/third_party/WebKit/LayoutTests/virtual/service-worker-navigation-preload-disabled/webexposed/global-interface-listing-expected.txt
[modify] https://crrev.com/868006705aed11538a1402f4db46953e2cfe2a5a/third_party/WebKit/LayoutTests/virtual/service-worker-navigation-preload-disabled/webexposed/global-interface-listing-shared-worker-expected.txt
[modify] https://crrev.com/868006705aed11538a1402f4db46953e2cfe2a5a/third_party/WebKit/LayoutTests/virtual/stable/http/tests/serviceworker/webexposed/global-interface-listing-service-worker-expected.txt
[modify] https://crrev.com/868006705aed11538a1402f4db46953e2cfe2a5a/third_party/WebKit/LayoutTests/virtual/stable/webexposed/global-interface-listing-dedicated-worker-expected.txt
[modify] https://crrev.com/868006705aed11538a1402f4db46953e2cfe2a5a/third_party/WebKit/LayoutTests/virtual/stable/webexposed/global-interface-listing-shared-worker-expected.txt
[modify] https://crrev.com/868006705aed11538a1402f4db46953e2cfe2a5a/third_party/WebKit/LayoutTests/webexposed/global-interface-listing-dedicated-worker-expected.txt
[modify] https://crrev.com/868006705aed11538a1402f4db46953e2cfe2a5a/third_party/WebKit/LayoutTests/webexposed/global-interface-listing-expected.txt
[modify] https://crrev.com/868006705aed11538a1402f4db46953e2cfe2a5a/third_party/WebKit/LayoutTests/webexposed/global-interface-listing-shared-worker-expected.txt
[modify] https://crrev.com/868006705aed11538a1402f4db46953e2cfe2a5a/third_party/WebKit/Source/modules/push_messaging/PushSubscription.cpp
[modify] https://crrev.com/868006705aed11538a1402f4db46953e2cfe2a5a/third_party/WebKit/Source/modules/push_messaging/PushSubscription.h
[modify] https://crrev.com/868006705aed11538a1402f4db46953e2cfe2a5a/third_party/WebKit/Source/modules/push_messaging/PushSubscription.idl