[chromium_src] Allow overrides to reference original files with #include <...>
This change updates the include path handling for brave/chromium_src overrides:
- Adds support for referencing original Chromium files using #include <...> in
overrides.
- Enables this by replacing -I../../brave/chromium_src with
-iquote../../brave/chromium_src, so the path is only used for #include "..."
directives.
With this, other files in the build tree can reference brave/chromium_src
overrides using #include "...", while the overrides themselves can reference
original Chromium files using #include <...>. Since Chromium uses #include "..."
for all in-tree files, we can leverage this convention and eventually drop
support for #include "src/" by removing -I../../.. and making rbe_exec_root
modification obsolete.
Aleksei Khoroshilov
6dafba18f8