In order to be able to use SwiftShader on the bots, use_egl must be true
so that the EGL codepath is compiled into the executable.

This increases the official build size by about 44KB.

Bug:chromium:757974 chromium:726075 chromium:549742

Cq-Include-Trybots: luci.chromium.try:android_optional_gpu_tests_rel;luci.chromium.try:linux_optional_gpu_tests_rel;luci.chromium.try:mac_optional_gpu_tests_rel;luci.chromium.try:win_optional_gpu_tests_rel;master.tryserver.blink:linux_trusty_blink_rel;master.tryserver.chromium.linux:linux_layout_tests_slimming_paint_v2
Change-Id: I21c254a877eda89edb74de879a0c8d5c16ca16b3
Reviewed-on: https://chromium-review.googlesource.com/1005017
Commit-Queue: Alexis Hétu <sugoi@chromium.org>
Reviewed-by: Zhenyao Mo <zmo@chromium.org>
Reviewed-by: Kenneth Russell <kbr@chromium.org>
Cr-Commit-Position: refs/heads/master@{#559945}