Document UMA histograms for app launcher discoverability.

To track effectiveness of the app launcher install education pages in
enabling users to find, and start using, the app launcher when it is
auto-enabled upon installing the first v2 packaged app from the Web
Store.

Histogram recording committed in http://crrev.com/250348.

BUG=314235

Review URL: https://codereview.chromium.org/156963005

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@251254 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 251254
Fix output string of pepper_hash_for_uma.

So that the string can be directly copied into histograms.xml.

BUG=111542

Review URL: https://codereview.chromium.org/164253002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@251255 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 251255
Support for new data reduction proxy via header

This new header conforms to RFC 2616. With this change,
both the old and new header will be supported. Eventually,
support for the old header will be removed.

BUG=340333

Review URL: https://codereview.chromium.org/156373002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@251256 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 251256