It looks like Chrome now has this feature via Chrome developer tools (Ctrl-Shift-I). Click on the "Device Mode" icon at the top-left. Now, a device and network bandwidth and latency (or completely offline) can be simulated using the dropdowns at the top of the screen:
The screenshot above is from Chrome Version 42.0.2311.60 beta (64-bit) on Linux.
NOTE: As of Apr 2015, unfortunately this does not affect Websocket connections, which continue to operate regardless of the Network setting. See https://code.google.com/p/chromium/issues/detail?id=423246.
UPDATE Sep 2021: It looks like the network settings will finally affect websocket connections as of Chrome 96. See the issue above for details.