Previously, a struct (anonymous or named) whose fields all matched the
predicate would not be sharded and would simply be reused. However,
that could break the maxNameSize limitation which could cause problems
for the caller.
This change makes sure that the supplied struct is only reused if it
does not exceed the maxNameSize, and otherwise is sharded.
Bug: 183777071
Test: m nothing
Change-Id: I8af272ec121077a43333e72b67cfd0e493c83362
2aa510c27b