Enable Oculus devices behind a runtime flag

This change moves the Oculus device to be behind a runtime flag, rather
than a build flag.  It will only be enabled if is_chrome_branding,
is_win, and src_internal is available.

The means that developers testing with Oculus support should still build
locally with enable_oculus_vr gn arg if they aren't building with chrome
branding.

Public bots (CQ) will not build this, but perftests/fyi will.

BUG=812050

Change-Id: I7b99d98b53adf8878c0523e2eafe4ab422936ebe
Reviewed-on: https://chromium-review.googlesource.com/917644
Reviewed-by: Dirk Pranke <[email protected]>
Reviewed-by: Brandon Jones <[email protected]>
Commit-Queue: Bill Orr <[email protected]>
Cr-Commit-Position: refs/heads/master@{#536817}
diff --git a/chrome/browser/flag_descriptions.h b/chrome/browser/flag_descriptions.h
index e9bddd9..bb0d09d 100644
--- a/chrome/browser/flag_descriptions.h
+++ b/chrome/browser/flag_descriptions.h
@@ -1781,6 +1781,11 @@
 
 #endif  // OS_ANDROID
 
+#if BUILDFLAG(ENABLE_OCULUS_VR)
+extern const char kOculusVRName[];
+extern const char kOculusVRDescription[];
+#endif  // ENABLE_OCULUS_VR
+
 #if BUILDFLAG(ENABLE_OPENVR)
 extern const char kOpenVRName[];
 extern const char kOpenVRDescription[];