Fill SkRRect::fType proactively.

I found no external mentions of SkRRect::kUnknown_Type.

Motivating race found by TSAN:
http://build.chromium.org/p/client.skia/builders/Test-Ubuntu13.10-GCE-NoGPU-x86_64-Release-TSAN-Trybot/builds/48/steps/dm/logs/stdio

BUG=skia:

Review URL: https://codereview.chromium.org/801693003
4 files changed