Centralize the calculation to SkGlyphCacheCommon. This allows this
function to be used with NO_GPU.
In addition, this was used in the last remaining function in GrTest.
That function was used in a single place. I made the function a static
and remove GrTest.h. This had massive knock-on effects.
Change-Id: I80f874a988f9af4383a83acf7c273d23b8d67c22
Reviewed-on: https://skia-review.googlesource.com/151480
Reviewed-by: Jim Van Verth <jvanverth@google.com>
Commit-Queue: Herb Derby <herb@google.com>
