Add ServiceManager::GetInstance() and change ServiceManager::Loader to ServiceLoader

BUG=None
TESTS=Existing
R=darin@chromium.org, darin

Review URL: https://codereview.chromium.org/185553012

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@254783 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 254783
Fix warning when building remoting_webapp

The warning about unused PRODUCT_DESCRIPTION resource
was introduced in r254355.

R=jamiewalch@chromium.org

Review URL: https://codereview.chromium.org/184823010

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@254784 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 254784