[jumbo] undef SHADER macros after using them

Several files in gpu/command_buffer/service use local SHADER
macros. If they are compiled together in a jumbo build those
macros will collide and prevent the compilation.

This patch undefs the macros after use. An alternative is to
give them unique names.

Bug: 864986
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: I9de4011e1d609e5658a9d6cbe1775a3146364fa1
Reviewed-on: https://chromium-review.googlesource.com/1143265Reviewed-by: Antoine Labour <piman@chromium.org>
Commit-Queue: Daniel Bratell <bratell@opera.com>
Cr-Commit-Position: refs/heads/master@{#577044}

gpu/command_buffer/service/gles2_cmd_apply_framebuffer_attachment_cmaa_intel.cc

@@ -1847,3 +1847,5 @@ const char ApplyFramebufferAttachmentCMAAINTELResourceManager::cmaa_frag_s2_[] =
 
 }  // namespace gles2
 }  // namespace gpu
+
+#undef SHADER

gpu/command_buffer/service/gles2_cmd_clear_framebuffer.cc

@@ -34,6 +34,7 @@ const char* g_fragment_shader_source = {
     }
   ),
 };
+#undef SHADER
 
 }  // namespace