Fix destruction thread DCHECK in ContextProviderCommandBuffer

We allowed destruction on main thread for historical reasons. Update
DCHECK to represent the real requirement, that we're always destroyed
on the bound thread.

Bug: 899395
Change-Id: I542ecbd2bbdb449b96bed2b7f747640873847e15
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2029491
Auto-Submit: Eric Karl <ericrk@chromium.org>
Reviewed-by: Khushal <khushalsagar@chromium.org>
Commit-Queue: Khushal <khushalsagar@chromium.org>
Cr-Commit-Position: refs/heads/master@{#736714}

services/viz/public/cpp/gpu/context_provider_command_buffer.cc

@@ -82,8 +82,7 @@ ContextProviderCommandBuffer::ContextProviderCommandBuffer(
 }
 
 ContextProviderCommandBuffer::~ContextProviderCommandBuffer() {
-  DCHECK(main_thread_checker_.CalledOnValidThread() ||
-         context_thread_checker_.CalledOnValidThread());
+  DCHECK(context_thread_checker_.CalledOnValidThread());
 
   if (bind_tried_ && bind_result_ == gpu::ContextResult::kSuccess) {
     // Clear the lock to avoid DCHECKs that the lock is being held during