ES31: Support memoryBarrier and memoryBarrierRegion APIs

BUG=angleproject:2280
TEST=dEQP-GLES31.functional.compute.basic.image_barrier_single
     dEQP-GLES31.functional.compute.basic.image_barrier_multiple
     dEQP-GLES31.functional.compute.basic.ssbo_cmd_barrier_single
     dEQP-GLES31.functional.compute.basic.ssbo_cmd_barrier_multiple
     dEQP-GLES31.functional.synchronization.*

Change-Id: If14debab21247dc4b446e86d1642fbc9376b6dd7
Reviewed-on: https://chromium-review.googlesource.com/798803
Commit-Queue: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Jamie Madill <jmadill@chromium.org>
diff --git a/src/libANGLE/Context.cpp b/src/libANGLE/Context.cpp
index ade792e..bcccfc6 100644
--- a/src/libANGLE/Context.cpp
+++ b/src/libANGLE/Context.cpp
@@ -4277,12 +4277,12 @@
 
 void Context::memoryBarrier(GLbitfield barriers)
 {
-    UNIMPLEMENTED();
+    handleError(mImplementation->memoryBarrier(this, barriers));
 }
 
 void Context::memoryBarrierByRegion(GLbitfield barriers)
 {
-    UNIMPLEMENTED();
+    handleError(mImplementation->memoryBarrierByRegion(this, barriers));
 }
 
 GLenum Context::checkFramebufferStatus(GLenum target)