BUILD.gn: Add temporary proxy groups for test targets

This will allow use to update gn_isolate_map_pyl to point to the groups
instead of the targets, while we move the actual targets in a different
file.

BUG=chromium:913171

Change-Id: Ic681fb12d9cbc99557b742784f5b1bf779b76ed1
Reviewed-on: https://dawn-review.googlesource.com/c/3100
Reviewed-by: Stephen White <senorblanco@chromium.org>
Reviewed-by: Corentin Wallez <cwallez@chromium.org>
Commit-Queue: Corentin Wallez <cwallez@chromium.org>

BUILD.gn

@@ -903,6 +903,17 @@ test("dawn_end2end_tests") {
   }
 }
 
+# Temporary groups to make a 5-way patch to fix crbug.com/913171
+group("dawn_unittests_temp_group") {
+  testonly = true
+  deps = [ ":dawn_unittests" ]
+}
+
+group("dawn_end2end_tests_temp_group") {
+  testonly = true
+  deps = [ ":dawn_end2end_tests" ]
+}
+
 ###############################################################################
 # Dawn samples, only in standalone builds
 ###############################################################################