Fix glDeleteTextures called without context

When we don't have a current context, g_current_gl_context is not null.
Instead, it's an instance of NoContextGLApi. In ExternalVkImageBacking
::Destroy, don't check that g_current_gl_context is null. Always call
MakeCurrent.

Bug: 939442
Change-Id: Icc4cc15daec78f32697d56cc102718cf5b0a229b
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1754708Reviewed-by: Peng Huang <penghuang@chromium.org>
Commit-Queue: Saman Sami <samans@chromium.org>
Cr-Commit-Position: refs/heads/master@{#687257}

gpu/command_buffer/service/external_vk_image_backing.cc

@@ -457,8 +457,7 @@ void ExternalVkImageBacking::Destroy() {
   if (texture_) {
     // Ensure that a context is current before removing the ref and calling
     // glDeleteTextures.
-    if (!gl::g_current_gl_context)
-      context_state()->MakeCurrent(nullptr, true /* need_gl */);
+    context_state()->MakeCurrent(nullptr, true /* need_gl */);
     texture_->RemoveLightweightRef(have_context());
   }
 }