rename SkDrawable to SkADrawable

BUG=skia:

Review URL: https://codereview.chromium.org/764463002
diff --git a/src/animator/SkDisplayEvent.cpp b/src/animator/SkDisplayEvent.cpp
index a0cfcb1..b5dc8145 100644
--- a/src/animator/SkDisplayEvent.cpp
+++ b/src/animator/SkDisplayEvent.cpp
@@ -130,7 +130,7 @@
         SkDisplayable* displayable = fChildren[index];
         if (displayable->isGroup()) {
             SkTDDrawableArray* parentList = displayList.getDrawList();
-            *parentList->append() = (SkDrawable*) displayable;  // make it findable before children are enabled
+            *parentList->append() = (SkADrawable*) displayable;  // make it findable before children are enabled
         }
         if (displayable->enable(maker))
             continue;
@@ -138,7 +138,7 @@
             return true;
         if (displayable->isDrawable() == false)
             return true;    // error
-        SkDrawable* drawable = (SkDrawable*) displayable;
+        SkADrawable* drawable = (SkADrawable*) displayable;
         SkTDDrawableArray* parentList = displayList.getDrawList();
         *parentList->append() = drawable;
     }