ozone-x11: Always initialize in multi-thread mode.

Like single-process mode, chrome uses x11 from multiple threads in
--mus mode too (the window-server thread, and the viz thread). So
always initialize ozone-x11 in multi-thread mode. It would be possible
to introduce a new flag in InitParams for this mode, but considering
this is only used for development purposes on developer workstation,
just init multi-thread mode unconditionally.

BUG=786453, 791619

Change-Id: I930fc325ef1a52f531a419f660d31f55af03d1c6
Reviewed-on: https://chromium-review.googlesource.com/809943Reviewed-by: Scott Violet <sky@chromium.org>
Commit-Queue: Sadrul Chowdhury <sadrul@chromium.org>
Cr-Commit-Position: refs/heads/master@{#521933}

ui/ozone/platform/x11/ozone_platform_x11.cc

@@ -114,9 +114,9 @@ class OzonePlatformX11 : public OzonePlatform {
     if (common_initialized_)
       return;
 
-    // In single process mode XInitThreads() must be the first Xlib call.
-    if (params.single_process)
-      XInitThreads();
+    // Always initialze in multi-thread mode, since this is used only during
+    // development.
+    XInitThreads();
 
     ui::SetDefaultX11ErrorHandlers();