Remove NaCl toolchains from the output dir (crbug.com/456902)
CLobber all to fix GN breakage (crbug.com/736215)
The Great Blink mv for source files (crbug.com/768828)
+Clobber to workaround buggy .ninja_deps cycle (crbug.com/934404)
+Clobber to flush stale generated files. See crbug.com/1406628
+Clobber to flush old .ninja_log files for updating ninja. See crbug.com/1406628#c14