Fix missing BGRA_EXT in format DCHECK

This DCHECK was triggering on debug cast build while using
a port of PartialMagnificationController.

Bug: none
Test: manual
Cq-Include-Trybots: luci.chromium.try:android_optional_gpu_tests_rel
Change-Id: I31273be8602f5e9bf9a114d91119cf7b9b374d87
Reviewed-on: https://chromium-review.googlesource.com/1110024Reviewed-by: Antoine Labour <piman@chromium.org>
Reviewed-by: Daniel Nicoara <dnicoara@chromium.org>
Commit-Queue: Ryan Daum <rdaum@chromium.org>
Cr-Commit-Position: refs/heads/master@{#569592}

components/viz/service/display/gl_renderer.cc

@@ -763,7 +763,12 @@ GLenum GLRenderer::GetFramebufferCopyTextureFormat() {
     format = GLCopyTextureInternalFormat(BackbufferFormat());
   // Verify the format is valid for GLES2's glCopyTexSubImage2D.
   DCHECK(format == GL_ALPHA || format == GL_LUMINANCE ||
-         format == GL_LUMINANCE_ALPHA || format == GL_RGB || format == GL_RGBA)
+         format == GL_LUMINANCE_ALPHA || format == GL_RGB ||
+         format == GL_RGBA ||
+         (output_surface_->context_provider()
+              ->ContextCapabilities()
+              .texture_format_bgra8888 &&
+          format == GL_BGRA_EXT))
       << format;
   return format;
 }