Make gm use SkFlags.

Make gm use SkFlags.

Make flag parser its own project. It is still in the tools folder,
but can now be used by other projects.

Some changes to behavior in order to work with SkFlags:
enable-missing-warning and disable-missing-warning have become
enableMissingWarning and noenableMissingWarning.

exclude-config is now excludeConfig

--config now can only be listed once, but all configs listed
after it will be included (same with excludeConfig and match).

In addition, writeJsonSummary has been changed to
writeJsonSummaryPath for consistency with other path flags.

Provide an option to SkFlags to provide a short name, and use
it for the flags which have short names.

--tileGridReplayScales now takes space separated arguments,
like other inputs.

BUG=https://code.google.com/p/skia/issues/detail?id=1094

Review URL: https://codereview.chromium.org/12632015

git-svn-id: http://skia.googlecode.com/svn/trunk@8235 2bbb7eff-a529-9590-31e7-b0007b416f81