Remove ContainsOnlyWhitespace from string_util and CollapseWhitespace into to the base namespace

This function is only used in a few places and can trivially be implemented by passing the whitespace constant to the existing ContainsOnlyChars function.

This changes the ContainsOnlyChars function signature to take a StringPiece to avoid a copy from a literal to a standard string in the above-mentioned use-base.

Re-implement ContainsOnlyChars to use the find_first_not_of function on StringPiece.

BUG=
R=viettrungluu@chromium.org

Review URL: https://codereview.chromium.org/183683024

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@256354 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 256354
Add content/renderer/shared_worker/OWNERS.

In this directory, we will implement the renderer side code for the SharedWorker in the renderer process.

BUG=327256

Review URL: https://codereview.chromium.org/194063004

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@256355 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 256355