Fix image wallpaper distortion after rotate.

Keep surface size large enough to draw the image.
When we shrink for small image, we still maintain its aspect ratio.

Fix: 123108383
Test: atest ImageWallpaperTest
Test: manual verify aspect ratio not changed after rotate.
Test: manual put a small image as wallpaper and see surface size won't
grow too much.

Change-Id: Icf3bc4a3129d9aecba2b57c620f378b9d9d7374b