This is an outdated link to something discussed on Tom's Hardware that went a little into Flash performance across a few (now dated) browsers so the numbers are just a historic reference now and not to be considered updated/current data. So historically speaking, Chrome appears, at least back then, that Flash CPU usage is on par with some of the lowest to include Safari and Firefox/IE8 have had higher instances of CPU usage.
Source: http://www.tomshardware.com/reviews/adobe-flash-10.1-performance-hardware-acceleration,2805-7.html
Playback: YouTube 1080p on Asus UL20A
Aero Enabled, Hardware Acceleration Enabled
CPU Usage: Windowed
IE8 32-bit: 8.0.7600.1685 35%
Firefox: 3.6.12 49%
Opera: 10.63 (build 3516) 25%
Chrome: 8.0.552.215 28%
Safari: 5.0.3 26%
==========
Playback: YouTube 1080p on Asus UL20A
Aero Enabled, Hardware Acceleration Enabled
Fullscreen
IE8 32-bit: 8.0.7600.1685
CPU Usage: 52%
27.0 FPS
Firefox: 3.6.12 CPU Usage: 60%
27.8 FPS
Opera: 10.63 (build 3516) CPU Usage: 37%
15.5 FPS
Chrome: 8.0.552.215 CPU Usage: 39%
14.0 FPS
Safari: 5.0.3 CPU Usage: 39%
13.8 FPS
During that time, the one thing I can pretty much state is that Firefox appears to have the highest CPU usage among the rest.
I would like to point out look at the FPS. FF had the highest FPS followed close by IE. Both of which blow the rest out of the water by a healthy margin.