Revert 255357 "Change the user action file format from .txt to ...."

Believed to be behind the failures in the Linux builder:

http://build.chromium.org/p/chromium/builders/Linux/builds/47996

Errors in the log:

.../actions/print_style.py: Has executable bit but not shebang or ELF header
.../histograms/print_style.py: Has executable bit but not shebang or ELF header

Refers to files in the CL.

> Change the user action file format from .txt to .xml.
>
> In this way, more information can be added (currently added 'description' and 'owner' for each action)
>
> A few functions are moved from tools/metrics/histograms to tools/metrics/common to be shared by tools/metrics and tools/histograms.
>
> BUG=340735
> NOTRY=true
>
> Review URL: https://codereview.chromium.org/149503005

TBR=yiyaoliu@chromium.org

Review URL: https://codereview.chromium.org/188793003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@255404 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 255404