I tried to follow the document to build electron on a fresh clean built Ubuntu 15.04.
I encountered the following error message when trying to run ./script/bootstrap.py -v
Package nss was not found in the pkg-config search path.
Perhaps you should add the directory containing `nss.pc'
to the PKG_CONFIG_PATH environment variable
No package 'nss' found
After installing libnss3-dev, the build can pass.