Rename "register" -> "subscribe" in the Push Messaging code.

Rename "register" -> "subscribe" in the Push Messaging code.

This is a mechanical change from "register" to the new keyword
"subscribe", matching terminology of the Web Push protocol, the W3C
Push API and GCM, the push service we use.

UMA, preferences and Web exposed values are being left untouched.

BUG=446883

[Peter Beverloo, 2015-05-06 20:07:02]

peter@chromium.org changed reviewers:
+ johnme@chromium.org

[Peter Beverloo, 2015-05-06 20:07:03]

--> johnme

[johnme, 2015-05-07 13:31:26]

lgtm with nits.

> UMA, preferences and Web exposed values are being left untouched.

Please also rename the UMA enums to match - since you won't change the ordinals,
it shouldn't break existing metrics.

https://codereview.chromium.org/1129833003/diff/1/chrome/browser/push_messagi...
File chrome/browser/push_messaging/push_messaging_service_impl.cc (right):

https://codereview.chromium.org/1129833003/diff/1/chrome/browser/push_messagi...
chrome/browser/push_messaging/push_messaging_service_impl.cc:193: // Drop
message and unsibscribe if app id was unknown (recently deleted?).
Typo

https://codereview.chromium.org/1129833003/diff/1/chrome/browser/push_messagi...
File chrome/browser/push_messaging/push_messaging_service_impl.h (right):

https://codereview.chromium.org/1129833003/diff/1/chrome/browser/push_messagi...
chrome/browser/push_messaging/push_messaging_service_impl.h:75: override;
Nit: Same indent as previous line.

https://codereview.chromium.org/1129833003/diff/1/chrome/browser/push_messagi...
chrome/browser/push_messaging/push_messaging_service_impl.h:82: override;
Nit: Same indent as previous line.

https://codereview.chromium.org/1129833003/diff/1/chrome/browser/push_messagi...
chrome/browser/push_messaging/push_messaging_service_impl.h:168: // Subscription
methods ------------------------------------------------------
Nit: "Subscribe methods" for consistency

https://codereview.chromium.org/1129833003/diff/1/content/browser/push_messag...
File content/browser/push_messaging/push_messaging_message_filter.cc (right):

https://codereview.chromium.org/1129833003/diff/1/content/browser/push_messag...
content/browser/push_messaging/push_messaging_message_filter.cc:210: //
Subscription methods on both IO and UI threads, merged in order of use from
Nit: "Subscribe" for consistency (even though it's slightly less grammatical)

https://codereview.chromium.org/1129833003/diff/1/content/browser/push_messag...
File content/browser/push_messaging/push_messaging_message_filter.h (right):

https://codereview.chromium.org/1129833003/diff/1/content/browser/push_messag...
content/browser/push_messaging/push_messaging_message_filter.h:82: const
std::string& push_subscribe_id);
Nit: "push_subscription_id"

https://codereview.chromium.org/1129833003/diff/1/content/public/common/push_...
File content/public/common/push_messaging_status.cc (right):

https://codereview.chromium.org/1129833003/diff/1/content/public/common/push_...
content/public/common/push_messaging_status.cc:21: return "Registration failed -
no Service Worker";
Please also rename all these strings. Since the web-facing API is
subscribe/unsubscribe, the error messages should talk about
subscription/unsubscription as well.