ozone: Initialize a subsystem only if necessary.

content/browser/browser_main_loop.cc

Index: content/browser/browser_main_loop.cc
diff --git a/content/browser/browser_main_loop.cc b/content/browser/browser_main_loop.cc
index ad00ac03f52034e56470d9ecedce767d17f6fad5..a30a62eff7e81dfd7c6c34f6ace51bb64cd01c01 100644
--- a/content/browser/browser_main_loop.cc
+++ b/content/browser/browser_main_loop.cc
@@ -122,10 +122,6 @@
 #include "ui/gfx/x/x11_types.h"
 #endif
 
-#if defined(USE_OZONE)
-#include "ui/ozone/ozone_platform.h"
-#endif
-
 // One of the linux specific headers defines this as a macro.
 #ifdef DestroyAll
 #undef DestroyAll
@@ -958,10 +954,6 @@ int BrowserMainLoop::BrowserThreadsStarted() {
   device_monitor_mac_.reset(new DeviceMonitorMac());
 #endif
 
-#if defined(USE_OZONE)
-  ui::OzonePlatform::Initialize();
-#endif
-
   // RDH needs the IO thread to be created
   {
     TRACE_EVENT0("startup",