When the Database process was renamed to the Storage process (<http://trac.webkit.org/changeset/220094>), the name of the sandbox was changed but the actual sandbox file was not renamed. The preprocessing steps to generate the sandbox profile were also not updated for the new naming.
<rdar://problem/37046844>
I guess this should be "Part 4 of: Rename DatabaseProcess to StorageProcess" :-)
Created attachment 332807 [details] Patch
Committed r227939: <https://trac.webkit.org/changeset/227939>
Follow-up fix: Committed r227941: <https://trac.webkit.org/changeset/227941>