Set glFlush workaround in the GLES command decoder

This allows Nyan to force glFlush() based on the blacklist since
EGL_IMAGE_EXTERNAL_FLUSH_EXT is broken on NVIDIA.

Bug: 833975, 978206
Test: Ran on nyan board to validate no corruption.
Change-Id: Ib229422ec770a401369cf51b882e15c13a34f376
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1678381Reviewed-by: Daniele Castagna <dcastagna@chromium.org>
Reviewed-by: Antoine Labour <piman@chromium.org>
Commit-Queue: Daniel Nicoara <dnicoara@chromium.org>
Cr-Commit-Position: refs/heads/master@{#672543}

gpu/command_buffer/service/gles2_cmd_decoder.cc

@@ -3530,6 +3530,9 @@ gpu::ContextResult GLES2DecoderImpl::Initialize(
   if (workarounds().rely_on_implicit_sync_for_swap_buffers)
     surface_->SetRelyOnImplicitSync();
 
+  if (workarounds().force_gl_flush_on_swap_buffers)
+    surface_->SetForceGlFlushOnSwapBuffers();
+
   // Create GPU Tracer for timing values.
   gpu_tracer_.reset(new GPUTracer(this));