MediaRouter: Cache MediaRoutesObserver queries to prevent ext wake-ups

MediaRouter: Cache MediaRoutesObserver queries to prevent ext wake-ups

Resolved a performance issue where the Media Router component extension
was being woken-up each time a new tab was opened. The solution is to
cache route list updates so that the registration of new observers does
not force the extension to wake-up to report on something we can cache
browser-side. (This is the same as what is already being done for the
MediaSinksObservers.)

BUG=621246
TEST=Ran chrome with --enable-logging=stderr --vmodule=media_router_mojo_impl=1 to confirm extension wake-ups do not happen when opening new tabs.

Review-Url: https://codereview.chromium.org/2735493002
Cr-Commit-Position: refs/heads/master@{#454769}
(cherry picked from commit 34e86af9f3ebe792b7681053eca4c08b27eca52d)

Review-Url: https://codereview.chromium.org/2728293003 .
Cr-Commit-Position: refs/branch-heads/3029@{#26}
Cr-Branched-From: 939b32ee5ba05c396eef3fd992822fcca9a2e262-refs/heads/master@{#454471}
Committed: https://chromium.googlesource.com/chromium/src/+/ea43cd3d503c13abfa3f15ed97a4db1b1f37dcb0

[miu, 2017-03-06 21:03:46]

Description was changed from

==========
MediaRouter: Cache MediaRoutesObserver queries to prevent ext wake-ups

Resolved a performance issue where the Media Router component extension
was being woken-up each time a new tab was opened. The solution is to
cache route list updates so that the registration of new observers does
not force the extension to wake-up to report on something we can cache
browser-side. (This is the same as what is already being done for the
MediaSinksObservers.)

BUG=621246
TEST=Ran chrome with --enable-logging=stderr --vmodule=media_router_mojo_impl=1
to confirm extension wake-ups do not happen when opening new tabs.

Review-Url: https://codereview.chromium.org/2735493002
Cr-Commit-Position: refs/heads/master@{#454769}
(cherry picked from commit 34e86af9f3ebe792b7681053eca4c08b27eca52d)
==========

to

==========
MediaRouter: Cache MediaRoutesObserver queries to prevent ext wake-ups

Resolved a performance issue where the Media Router component extension
was being woken-up each time a new tab was opened. The solution is to
cache route list updates so that the registration of new observers does
not force the extension to wake-up to report on something we can cache
browser-side. (This is the same as what is already being done for the
MediaSinksObservers.)

BUG=621246
TEST=Ran chrome with --enable-logging=stderr --vmodule=media_router_mojo_impl=1
to confirm extension wake-ups do not happen when opening new tabs.

Review-Url: https://codereview.chromium.org/2735493002
Cr-Commit-Position: refs/heads/master@{#454769}
(cherry picked from commit 34e86af9f3ebe792b7681053eca4c08b27eca52d)

Review-Url: https://codereview.chromium.org/2728293003 .
Cr-Commit-Position: refs/branch-heads/3029@{#26}
Cr-Branched-From:
939b32ee5ba05c396eef3fd992822fcca9a2e262-refs/heads/master@{#454471}
Committed:
https://chromium.googlesource.com/chromium/src/+/ea43cd3d503c13abfa3f15ed97a4...
==========

[miu, 2017-03-06 21:03:48]

Committed patchset #1 (id:1) manually as
ea43cd3d503c13abfa3f15ed97a4db1b1f37dcb0.