Chrome is a good O.S. for web, but be prepared, the Chromebooks in general compromise a lot due to their price. So basically, you're going to get a very low-end, cheaply built, slow computer for that price, regardless of what you go with.
I've used the Samsung Chromebook running the Arm processor and I loved it. I kinda want to get one just to play around with, but both it and the Acer or any other $300 Windows 8 laptop will bog down on 720p video if anything else is running. Whether it be Tabs in the browser, IM, video or audio chats, music or even a player being launched. You're going to see stutter or flat out pauses in the frame rate of the video. As the computer ages, it will slow somewhat, and this problem will worsen.
Another $20-$60 and you get into the range of the Pentium and i3 processors. While you'll still get a cheaply built computer, you'll at least get the capability of playing HD video streaming.