In order to implement the --use-gl=angle Chrome flag on Linux, we need
to have the ANGLE .so directly in the build directory however GYP
places shared_libraries under lib/ on Linux. On the contrary loadable_modules
cannot be linked against so we need to keep the shared_library targets.

This commit adds _ANGLE versions of the libEGL and libGLESv2 targets as
loadable module that depend on their respective shared library.

BUG=522967

Change-Id: I08f2ce0ee0430eff5bee852f09cd7d30b94d6266
Reviewed-on: https://chromium-review.googlesource.com/316421Reviewed-by: Jamie Madill <jmadill@chromium.org>
Tested-by: Corentin Wallez <cwallez@chromium.org>
Tryjob-Request: Corentin Wallez <cwallez@chromium.org>
Reviewed-by: Kenneth Russell <kbr@chromium.org>