ui/ozone: runtime-map "gbm" platform to "drm"

CL crrev.com/c/2373181 renamed the gbm ozone platform to drm, but our
Tast video tests for Chrome OS still refer to the old name when
selecting the Ozone platform at runtime. Temporarily map "gbm" to "drm"
to avoid tests breakage until we switch to the new name.

BUG=b:169115289
BUG=1116466
TEST=video.EncodeAccel.h264_360p_i420 passes on Kukui.

Change-Id: Idd8775b30ec07fa5af0c19d4e1a624846b9fe2fd
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2423443
Commit-Queue: Alexandre Courbot <acourbot@chromium.org>
Auto-Submit: Alexandre Courbot <acourbot@chromium.org>
Reviewed-by: Daniele Castagna <dcastagna@chromium.org>
Reviewed-by: Miguel Casas <mcasas@chromium.org>
Reviewed-by: Michael Spang <spang@chromium.org>
Cr-Commit-Position: refs/heads/master@{#809640}

ui/ozone/platform_selection.cc

@@ -33,6 +33,9 @@ int GetOzonePlatformId() {
     return g_selected_platform;
 
   std::string platform_name = GetPlatformName();
+  // TODO(b/169115289) remove once all Tast tests use "drm".
+  if (platform_name == "gbm")
+    platform_name = "drm";
 
   // Search for a matching platform in the list.
   for (int platform_id = 0; platform_id < kPlatformCount; ++platform_id) {