Simplifying some environment madness. Nobody gets to modify default_env.
Always apply it in run.__call__(). Add depot_tools path to PATH in
default_env. Result is simpler but now default_env is applied in many
more places, which should be harmless.
BUG=skia:
Change-Id: I8299d50bde2bc3e2d47568a267d1d962a3fc3d56
Reviewed-on: https://skia-review.googlesource.com/9916
Reviewed-by: Ravi Mistry <rmistry@google.com>
Commit-Queue: Eric Boren <borenet@google.com>
bbb24f2ab8