Promote WEBGL_multi_draw extension out of draft

Per https://github.com/KhronosGroup/WebGL/pull/3113

Bug: 890539
Change-Id: I7d3c948babd43350c15e458e447d1d8a67063588
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2334104Reviewed-by: Kenneth Russell <kbr@chromium.org>
Commit-Queue: Shrek Shao <shrekshao@google.com>
Cr-Commit-Position: refs/heads/master@{#794306}

third_party/blink/renderer/modules/webgl/webgl2_rendering_context.cc

@@ -149,7 +149,7 @@ void WebGL2RenderingContext::RegisterContextExtensions() {
   RegisterExtension(webgl_draw_instanced_base_vertex_base_instance_,
                     kDraftExtension);
   RegisterExtension(webgl_lose_context_);
-  RegisterExtension(webgl_multi_draw_, kDraftExtension);
+  RegisterExtension(webgl_multi_draw_);
   RegisterExtension(webgl_multi_draw_instanced_base_vertex_base_instance_,
                     kDraftExtension);
   RegisterExtension(webgl_video_texture_, kDraftExtension);

third_party/blink/renderer/modules/webgl/webgl_rendering_context.cc

@@ -209,7 +209,7 @@ void WebGLRenderingContext::RegisterContextExtensions() {
   RegisterExtension(webgl_depth_texture_, kApprovedExtension, kBothPrefixes);
   RegisterExtension(webgl_draw_buffers_);
   RegisterExtension(webgl_lose_context_, kApprovedExtension, kBothPrefixes);
-  RegisterExtension(webgl_multi_draw_, kDraftExtension);
+  RegisterExtension(webgl_multi_draw_);
   RegisterExtension(webgl_video_texture_, kDraftExtension);
 }