Validate the build type argument value in function build_webrtc
Validate the build type argument value in function build_webrtc

BUG=None
NOTRY=True

Review-Url: https://codereview.webrtc.org/2655893003
Cr-Original-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#16277}
Cr-Mirrored-From: https://chromium.googlesource.com/external/webrtc
Cr-Mirrored-Commit: 1a7f01c6d32842de15d128d959a904edb85e4ded

Alkalyne/webrtctrunk,Alkalyne/webrtctrunk,Alkalyne/webrtctrunk,Alkalyne/webrtctrunk,Alkalyne/webrtctrunk,Alkalyne/webrtctrunk,Alkalyne/webrtctrunk,Alkalyne/webrtctrunk