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This is the first R/W operation. The new event in IDL has [nodoc], since we
don't want to show it on developer.chrome.com before most of the R/W features
are done.

TEST=unit_tests, browser_tests: *FileSystemProvider*CreateDirectory*
BUG=391362

Review URL: https://codereview.chromium.org/366263002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@282554 0039d316-1c4b-4281-b951-d872f2087c98