Sync MIN_SIZE_FOR_DIRECT_BLOBSTORE with the MIN_SIZE_FOR_BLOBSTORE in isolateserver.
Sync MIN_SIZE_FOR_DIRECT_BLOBSTORE with the MIN_SIZE_FOR_BLOBSTORE in isolateserver.

Eventually, it'd be preferable to not hardcode the value here and query
isolateserver instead, or make isolateserver smarter about it. For now, we have
to work with the current AppEngine limitations, including the 32 mb request
limit so a sensible limit is needed.

R=csharp@chromium.org
BUG=


Review URL: https://chromiumcodereview.appspot.com/11519034

git-svn-id: d5a9b8648c52d490875de6588c8ee7ca688f9ed1@172608 0039d316-1c4b-4281-b951-d872f2087c98

luci/luci-py,luci/luci-py,luci/luci-py,luci/luci-py