There is a known issue with using Pub dart in a corporate network using a proxy (on windows machine at least). You cannot even run the samples as they make use of pub to get
Another way to go is using the command line tools for getting the packages:
(On Windows)
Proxy Settings
In the cmd (not persistent):
SET HTTP_PROXY=proxy:port
SET HTTPS_PROXY=proxy:port
Or as Zdeslav Vojkovic suggested - specify system environment variables (persistent).
Go to the sample app folder
cd \samples\angular_todo\
Run the required pub command:
\dart-sdk\bin\pub.bat get
Project is automatically updated in the dart editor.
Edit: Try as well setting the proxy information as system environment variables, but using lower case e.g.
http_proxy=proxy:port
https_proxy=proxy:port
As far I as know Windows environment variables are not case sensitive. However dart editor seems to make difference.