If we attempt to compile the GLES1 emulation shader when the client
version is 1, we use the webgl 1 / GLES2 spec, not the GLES3 spec that
we use for GLES1 emulation.

This CL adds a case in Compiler.cpp for ES 1 contexts to use the higher
spec shader compiler.

BUG=angleproject:2306

Change-Id: I86fe534dd405279155bd81680fed77b8f9a09042
Reviewed-on: https://chromium-review.googlesource.com/925548Reviewed-by: Lingfeng Yang <lfy@google.com>
Reviewed-by: Geoff Lang <geofflang@chromium.org>
Commit-Queue: Lingfeng Yang <lfy@google.com>