Menlo Ventures, a totem of the powerful Sand Hill Road investing community that has backed almost every major Silicon Valley success story since the birth of the silicon chip, has raised a $400 million fund to back a new generation of tech startups, the firm announced Wednesday. The new fund will allow Menlo Ventures -- which has funded companies such as Uber, Tumblr and Gilead Sciences -- to continue its role as a heavyweight in what has become an ultracompetitive investing environment where funding rounds have reached never-before-seen levels.