rename SkDrawable to SkADrawable

BUG=skia:

Review URL: https://codereview.chromium.org/764463002
diff --git a/src/animator/SkTextToPath.h b/src/animator/SkTextToPath.h
index ac44ad7..9b72e5d 100644
--- a/src/animator/SkTextToPath.h
+++ b/src/animator/SkTextToPath.h
@@ -17,7 +17,7 @@
 class SkDrawPath;
 class SkText;
 
-class SkTextToPath : public SkDrawable {
+class SkTextToPath : public SkADrawable {
     DECLARE_MEMBER_INFO(TextToPath);
     SkTextToPath();
     virtual bool draw(SkAnimateMaker& );