media/gpu/test: Make GL context current in FrameRendererThumbnail

It is needed that a thread has made GL context current before
FrameRendererThumbnail::CreateVideoFrame() is called. Otherwise,
the gl functions called in CreateTexture() causes a segmentation
fault. But the test code doesn't fulfill this if it runs with
VaapiVDA.

This fixes the issue by making GL context current in
FrameRendererThumbnail::CreateVideoFrame().

Bug: 1037926
Test: VDA test on guado
Change-Id: I41e9778886d205196038deac17c1a84cc0874635
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1985738
Commit-Queue: Hirokazu Honda <hiroh@chromium.org>
Reviewed-by: David Staessens <dstaessens@chromium.org>
Cr-Commit-Position: refs/heads/master@{#728758}

media/gpu/test/video_player/frame_renderer_thumbnail.cc

@@ -225,6 +225,9 @@ scoped_refptr<VideoFrame> FrameRendererThumbnail::CreateVideoFrame(
     uint32_t* texture_id) {
   DCHECK_CALLED_ON_VALID_SEQUENCE(renderer_sequence_checker_);
 
+  // Make the GL context current in the case it's not currently yet.
+  AcquireGLContext();
+
   // Create a mailbox.
   gpu::Mailbox mailbox = gpu::Mailbox::Generate();
   gpu::MailboxHolder mailbox_holders[media::VideoFrame::kMaxPlanes];