Implement immutable texture base/max level clamping

It seems some drivers fail to handle that gracefully, so let's always clamp
to be on the safe side.

BUG=877874
TEST=test case in the bug, gpu_unittests
R=kbr@chromium.org

Cq-Include-Trybots: luci.chromium.try:android_optional_gpu_tests_rel;luci.chromium.try:linux_optional_gpu_tests_rel;luci.chromium.try:mac_optional_gpu_tests_rel;luci.chromium.try:win_optional_gpu_tests_rel
Change-Id: I6d93cb9389ea70525df4604112223604577582a2
Reviewed-on: https://chromium-review.googlesource.com/1194994
Reviewed-by: Kenneth Russell <kbr@chromium.org>
Commit-Queue: Zhenyao Mo <zmo@chromium.org>
Cr-Commit-Position: refs/heads/master@{#587264}
void GLES2DecoderImpl::DoCopyBufferSubData(GLenum readtarget,
                                           GLenum writetarget,
                                           GLintptr readoffset,
                                           GLintptr writeoffset,
                                           GLsizeiptr size) {
  buffer_manager()->ValidateAndDoCopyBufferSubData(
      &state_, readtarget, writetarget, readoffset, writeoffset, size);
}

void GLES2DecoderImpl::DoCopyBufferSubData(GLenum readtarget,
                                           GLenum writetarget,
                                           GLintptr readoffset,
                                           GLintptr writeoffset,
                                           GLsizeiptr size) {
  buffer_manager()->ValidateAndDoCopyBufferSubData(
      &state_, readtarget, writetarget, readoffset, writeoffset, size);
}
