This will make applications aware of device loss on all EGL calls that
need to have an initialized display. For that purpose, we track the
device loss state at the egl::Display level instead of always querying
the implementation. This is correct because at device-loss at the
display level is non-recoverable. It also deduplicates the tracking
that would have to be done in all the EGL backends.

Changes made in this commit:
 - Cached device loss in egl::Display
 - Check isDeviceLost in ValidateDisplay
 - Changed EGL entry-points testing isDeviceLost to explicitely request
   a testDeviceLost
 - Add calls to ValidateDisplay to entry-points missing it
 - Removed unused virtual qualifiers for some robustness methods

BUG=angleproject:1463

Change-Id: I92bea81f2ecd5423c445cff31557a4d9783557d5
Reviewed-on: https://chromium-review.googlesource.com/365450Reviewed-by: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Geoff Lang <geofflang@chromium.org>
Commit-Queue: Corentin Wallez <cwallez@chromium.org>