Reland 61124 - Disk Cache: Add a quick return path for truncating an empty stream and make sure that Flush() doesn't fail when it has nothing to do.
Reland 61124 - Disk Cache: Add a quick return path for truncating an empty stream
and make sure that Flush() doesn't fail when it has nothing to do.

BUG=56872, 57395
TEST=none

Review URL: http://codereview.chromium.org/3551005

Review URL: http://codereview.chromium.org/3576007

git-svn-id: dd90618784b6a4b323ea0c23a071cb1c9e6f2ac7@61183 4ff67af0-8c30-449e-8e8b-ad334ec8d88c

wistoch/meego-app-browser,wistoch/meego-app-browser,wistoch/meego-app-browser,wistoch/meego-app-browser,wistoch/meego-app-browser,wistoch/meego-app-browser,wistoch/meego-app-browser,wistoch/meego-app-browser,wistoch/meego-app-browser,wistoch/meego-app-browser