Add privet HTTP operation for reading file contents

Add a privet HTTP operation for reading the file contents, including the ability
to use range requests and save the contents to a file.

BUG=332182

Review URL: https://codereview.chromium.org/135513005

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@251402 0039d316-1c4b-4281-b951-d872f2087c98
Include the language (locale) info in the update ping
BUG=336614
TBR=thakis@chromium.org (since I "deleted" [read:moved] c/c/omaha/OWNERS, it needs an owner for those changes. cpu@ reviewed, deferred to sorin, who lg'd. But need an owner for CQ. Sorry for the convolution).

Review URL: https://codereview.chromium.org/153273002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@251403 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 251403