GitLab

* Fix dependency issues in //extensions
* Make protobuf library add the "src" directory to the compiler's include
  directory list, otherwise it tries to use /usr/include/google/protobuf
  which has incompatible headers.

BUG=455919
TEST=compiles and links in both component and non-component builds

Review URL: https://codereview.chromium.org/889253004

Cr-Commit-Position: refs/heads/master@{#315067}