Create ANGLE's real context with EGL_NO_CONFIG_KHR.
This allows ANGLE to advertise EGLConfigs which previously were hidden
due to incompatibility with ANGLE's context.

Also enable EGLContextCompatibilityTest on ES2_OPENGLES to test this.

BUG=angleproject:2468

Change-Id: I6fbbe01b4b93db7df39606980f0f58eb74b11e31
Reviewed-on: https://chromium-review.googlesource.com/1022088Reviewed-by: Jamie Madill <jmadill@chromium.org>
Commit-Queue: Yuly Novikov <ynovikov@chromium.org>