The simplest PipelineBarrier implementation is to call Renderer::synchronize().
This removes the synchronization mechanism from the draw commands, while still
allowing the tests to pass successfully.

Bug b/118619338

Change-Id: If7d9c14170db6f9a74a54c45a978d3ce78a1cdca
Reviewed-on: https://swiftshader-review.googlesource.com/c/25608Tested-by: Alexis Hétu <sugoi@google.com>
Kokoro-Presubmit: kokoro <noreply+kokoro@google.com>
Reviewed-by: Chris Forbes <chrisforbes@google.com>