Add PYTHONPATH entry for proto internal.
Add PYTHONPATH entry for proto internal.

Turns out my new protobuf internal entries are copied to the out dir,
so we need a new entry for that.

Tbr: d2c43c210eae6feef04f53bae50885e8152edcca@webrtc.org
Bug: chromium:1029452
Change-Id: I5bcae3a7ff1163e051382ae741646f206ccc7324
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/171869
Reviewed-by: Patrik Höglund <b486136ee68458b09c92c86c39f451c87d6ef6a1@webrtc.org>
Cr-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#30918}

ShiftMediaProject/libilbc,TimothyGu/libilbc,TimothyGu/libilbc,ShiftMediaProject/libilbc,ShiftMediaProject/libilbc,TimothyGu/libilbc,ShiftMediaProject/libilbc,TimothyGu/libilbc,ShiftMediaProject/libilbc,TimothyGu/libilbc