Relocate anisotropic mipmap logic to SkMipMap::extractLevel()

Pass a full x/y scale and defer the anisotropic heuristic to SkMipMap.

R=reed@google.com
GOLD_TRYBOT_URL= https://gold.skia.org/search2?unt=true&query=source_type%3Dgm&master=false&issue=1686563002

Review URL: https://codereview.chromium.org/1686563002
diff --git a/gm/showmiplevels.cpp b/gm/showmiplevels.cpp
index 7fc40ce..27d47e5 100644
--- a/gm/showmiplevels.cpp
+++ b/gm/showmiplevels.cpp
@@ -150,7 +150,7 @@
         int index = 0;
         SkMipMap::Level level;
         SkScalar scale = 0.5f;
-        while (mm->extractLevel(scale, &level)) {
+        while (mm->extractLevel(SkSize::Make(scale, scale), &level)) {
             SkBitmap bm = func(prevPM, level.fPixmap);
             DrawAndFrame(canvas, bm, x, y);
 
@@ -258,7 +258,7 @@
         int index = 0;
         SkMipMap::Level level;
         SkScalar scale = 0.5f;
-        while (mm->extractLevel(scale, &level)) {
+        while (mm->extractLevel(SkSize::Make(scale, scale), &level)) {
             SkBitmap bm;
             bm.installPixels(level.fPixmap);
             DrawAndFrame(canvas, bm, x, y);