drm: Don't block required overlays for consistency checks

This early exits from CanHandleCandidate which does checks to ensure
composited quads match up with overlay quads. If we are requiring the
use of an overlay, then skip those checks since we will never be
compositing that quad.

BUG=b:153111783,b:155511837
TEST=Required overlays render correctly, unit tests pass

Change-Id: Iad5d5eabd33cdc6bf2c4a3ba315b154eddaee3d3
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2593522
Commit-Queue: Jeffrey Kardatzke <jkardatzke@google.com>
Commit-Queue: Daniele Castagna <dcastagna@chromium.org>
Auto-Submit: Jeffrey Kardatzke <jkardatzke@google.com>
Reviewed-by: Daniele Castagna <dcastagna@chromium.org>
Cr-Commit-Position: refs/heads/master@{#837305}

ui/ozone/platform/drm/gpu/drm_overlay_manager.cc

@@ -149,9 +149,13 @@ bool DrmOverlayManager::CanHandleCandidate(
   if (candidate.transform == gfx::OVERLAY_TRANSFORM_INVALID)
     return false;
 
+  // The remaining checks are for ensuring consistency between GL compositing
+  // and overlays. If we must use an overlay, then skip the remaining checks.
+  if (candidate.requires_overlay)
+    return true;
+
   // Reject candidates that don't fall on a pixel boundary.
-  if (!candidate.requires_overlay &&
-      !gfx::IsNearestRectWithinDistance(candidate.display_rect, 0.01f))
+  if (!gfx::IsNearestRectWithinDistance(candidate.display_rect, 0.01f))
     return false;
 
   // DRM supposedly supports subpixel source crop. However, according to