NopCanvas is only hw accelerated during construction

During construction, we want to make NopCanvas as light as possible so
we just say that we are hw accelerated.
This caused some crashes further down the line for some views that
thought that NopCanvas was hw accelerated. From now on, NopCanvas is
only hw accelerated during construction.

Test: Covered by the existing tests
Change-Id: If09a662312e5c90d011e7ab2cbb524ef7b420d12