Ensure that all extensions are processed

Merge pull request ampproject#2625 from erwinmombay/fix-cyc-changelog

fix changelog to handle PR's that have a merge coming from master

Merge pull request ampproject#2566 from dvoytenko/access56

Ensure that pingback is executed when directly requested

Merge pull request ampproject#2502 from omegdadi/issue2491

Updated amp-fill-content to workaround IOS

Merge pull request ampproject#2429 from erwinmombay/fix-bug

remove reference to whenFirstLayoutCompleteResolve_

whitelist branches with the name amp-release-.* for a travis build

Merge pull request ampproject#2341 from cramforce/unique-canary

Turn on unique origins for dev channel by default.

Merge pull request ampproject#2312 from cramforce/typo

Fix crucial typo.

Merge tag '1456432550041' into release

Merge pull request ampproject#2284 from erwinmombay/dont-error-not-em…

…bedded

Reject messaging promise if not embedded.