Anti-alias thumbnail corners to look smoother

Thumbnail corners should be anti-aliased so that they look smoother and
less rough.

Bug: 131779031
Test: Manual, go to recents and see corners
Change-Id: I49a299671ec37f56b6eebe2dd2eb71790e8cb2b4
diff --git a/go/quickstep/src/com/android/quickstep/ThumbnailDrawable.java b/go/quickstep/src/com/android/quickstep/ThumbnailDrawable.java
index a8cc0a1..922e68a 100644
--- a/go/quickstep/src/com/android/quickstep/ThumbnailDrawable.java
+++ b/go/quickstep/src/com/android/quickstep/ThumbnailDrawable.java
@@ -57,6 +57,7 @@
         mCornerRadius = (int) res.getDimension(R.dimen.task_thumbnail_corner_radius);
         mShader = new BitmapShader(mThumbnailData.thumbnail, CLAMP, CLAMP);
         mPaint.setShader(mShader);
+        mPaint.setAntiAlias(true);
         updateMatrix();
     }