[inspector] disallow usage of non public api methods in inspector

Going forward we may relax this, but it is a conscious decision to be made.

BUG=chromium:635948
R=dgozman@chromium.org,alph@chromium.org

Review-Url: https://codereview.chromium.org/2337523003
Cr-Commit-Position: refs/heads/master@{#39362}

src/inspector/DEPS

+include_rules = [
+  "-src",
+  "+src/inspector",
+  "+src/base/macros.h",
+  "+src/base/logging.h"
+]