FileAPI: Return success when copying/moving file into the same path


BUG=329517
TEST=content_unittests --gtest_filter=FileSystemOperationImplTest.*

Review URL: https://codereview.chromium.org/118203003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@241828 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 241828