I was too darn curious and went ahead and bought a chromecast. The answer is: yes, it properly fits.
The mini usb port type b on the chromecast has been properly designed.
It is on the round side, opposite to the HDMI connector.
The port lays flat on the chromecast edge, with no bevels nor bezels: this cable connector plugs perfectly in the port and stays still.
A nice plus is that due to the short length and the mid/high wire gauge, this cable doesnt waste as much energy as some other cheap cables do (the chromecast power source is 850 mAh, a standard usb port gives 500 mAh. Using a cheap cable that is either too long or made with thin gauge wires would waste too much current turning it into heat due to resistance and it could cause power on failures or sudden shutdowns of the chromecast)
I would surely recommend this cable for chromecast usage. Just be sure that either the usb port is close enough to the hdmi connector to allow the end to bend and plug, and that your tv has enough mAh on the usb port to power it up (a quick failsafe test is to try plugging any usb only powered external hdd. If the hdd spins up and is being recognized, or at least spins up, there is enough current to keep a chromecast going)
---old answer, 4 jun 2014---
As far as i know the chromecast has a mini usb port to be powered. This cable adheres to mini usb plugs standard sizes: i have a galaxy s4 with official protection+ cover, which is cut tightly on the bottom to fit tightly a mini usb connector. It fits skintight without resistence.
I dont own a chromecast myself, but if there is a bezel around the power port or the port is right on the edge level, it should fit perfectly.