Docserver: Introduce an annotation to CompiledFileSystem's compilation function
which indicates it only relies on that data from a single file, not multiple
files. This allows implementing an optimisation where the file data doesn't need
to be re-compiled if the file stat is the same (note that it's never re-read because
CachingFileSystem already implements a similar optimisation).

This also replace a couple of uses of CompiledFileSystem.Create with the
appropriate CompileFileSystem.For* method.

BUG=305280
R=jyasskin@chromium.org
NOTRY=true

Review URL: https://codereview.chromium.org/54693004

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@232228 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 232228