Edited output of the timing code, see timing_code.diff for the actual code.

Option 1: Original 3.5.0 code:
Avg time 0.002 ms based on 29 thumbnails or medium-sized images.

Option 2: Proposed 3.5.1 code (Calling image_constrain_size_for_editor()):
Avg time 0.439 ms based on 29 thumbnails or medium-sized images.

Option 3: Equivalent 3.4 code (Calling image_downsize()):
Avg time 9.781 ms based on 29 thumbnails or medium-sized images.