[docs] Fix SkCanvas Creation API
[docs] Fix SkCanvas Creation API

The `encode` method of SkImage is renamed to `encodeToData` in
6409f84fc3ae5e3b2df9eb0a900957fce404ad5c.

We also don't use GrContext anymore. According to the file we included,
we should use GrDirectContext instead now.

This patch should make the code in the documentation buildable.

Change-Id: I07d27c5686673e17afb8a893b1c1c238fa84ecff
No-Try: true
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/554816
Commit-Queue: Brian Salomon <61fabaaf0876044aeedfd8e351e485c028d69e7b@google.com>
Reviewed-by: Brian Salomon <61fabaaf0876044aeedfd8e351e485c028d69e7b@google.com>

google/skia,google/skia,google/skia,google/skia,google/skia,google/skia,google/skia,google/skia,google/skia,google/skia