Use SkArenaAlloc in the SkAutoBlitterChoose code.

- Added default implementation of onMakeContext to support use in android.

Searches for uses:
"public SkShader"  package:^chromium$ -file:^src/third_party/skia
package:^aosp.* "public SkShader"  -file:external/skia -file:.*third_party/skia
package:^android$ "public SkShader"  -file:external/skia -file:.*third_party/skia

... shows that no subclass overrides onCreateContext.

TBR=reed@google.com
TBR=mtklein@google.com

Change-Id: I8bd5f57a79534574e344b165d31dccee41c31767
Reviewed-on: https://skia-review.googlesource.com/8140
Commit-Queue: Herb Derby <herb@google.com>
Reviewed-by: Herb Derby <herb@google.com>
49 files changed