Initialize three locals to avoid the risk of uninitialized reads.

Initialize three locals to avoid the risk of uninitialized reads.

/analyze recently reported two new warnings about reading from
potentially uninitialized local variables:

src\third_party\skia\src\gpu\grclipmaskmanager.cpp(290) :
warning C6001: Using uninitialized memory 'requiresAA'.
src\third_party\skia\src\gpu\grclipmaskmanager.cpp(336) :
warning C6001: Using uninitialized memory 'genID'.

It is not clear whether the uninitialized reads can actually happen,
but the guarantees seem sufficiently non-obvious that the prudent thing
to do to guarantee future stability is to initialized them -- it's
cheap. I also initialized initialState because it seemed to fall in
the same class, despite there being no warning for it.

BUG=427616

Review URL: https://codereview.chromium.org/957133002