RELAND: Ozone X11 check X display on initialization.

Add a CHECK that XOpenDisplay() doesn't return null when initializing
Ozone X11. There is no point going any further, we are going to crash
somewhere else and the crash stack isn't going to be as obvious.

Original change in https://crrev.com/c/980596. Reland change with call
to XInitThreaded() first still to avoid crashes.

Bug: 806508
Change-Id: I0ca480b140da702946b4b75cd93c63cd388fdfca
Reviewed-on: https://chromium-review.googlesource.com/997894Reviewed-by: Sadrul Chowdhury <sadrul@chromium.org>
Commit-Queue: kylechar <kylechar@chromium.org>
Cr-Commit-Position: refs/heads/master@{#548754}

ui/ozone/platform/x11/ozone_platform_x11.cc

@@ -108,15 +108,18 @@ class OzonePlatformX11 : public OzonePlatform {
  private:
   // Performs initialization steps need by both UI and GPU.
   void InitializeCommon(const InitParams& params) {
-    // TODO(kylechar): Add DCHECK we only enter InitializeCommon() twice for
-    // single process mode.
     if (common_initialized_)
       return;
 
-    // Always initialze in multi-thread mode, since this is used only during
+    // Always initialize in multi-thread mode, since this is used only during
     // development.
     XInitThreads();
 
+    // If XOpenDisplay() failed there is nothing we can do. Crash here instead
+    // of crashing later. If you are crashing here, make sure there is an X
+    // server running and $DISPLAY is set.
+    CHECK(gfx::GetXDisplay()) << "Missing X server or $DISPLAY";
+
     ui::SetDefaultX11ErrorHandlers();
 
     common_initialized_ = true;