Fix minigbm-using tests so that they require cros

This starts with //media/gpu/test:local_gpu_memory_buffer_manager
needing to use the chromeos-specific minigbm library.

Also then add a check for use_vaapi to the vaapi jpeg/webp decoder
unittests.

Change-Id: I3991961746bd6626b772f9143544c238d67b3dde
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2439780
Commit-Queue: Ted Meyer <tmathmeyer@chromium.org>
Reviewed-by: Andres Calderon Jaramillo <andrescj@chromium.org>
Reviewed-by: Dale Curtis <dalecurtis@chromium.org>
Cr-Commit-Position: refs/heads/master@{#813082}

media/gpu/test/BUILD.gn

@@ -214,7 +214,7 @@ if (use_vaapi || use_v4l2_codec) {
   }
 }
 
-if (is_chromeos || use_vaapi) {
+if (is_chromeos) {
   static_library("local_gpu_memory_buffer_manager") {
     testonly = true
     sources = [