[xr] Add a flag for enabling XR hit test support

Although there is no API yet, this flag will allow us to start working
on code that will support such an API in the future.

Bug: 830039
Change-Id: I770b210c088f6c231116e5a7660d4b49a18cdc96
Reviewed-on: https://chromium-review.googlesource.com/1000316
Commit-Queue: Ian Vollick <[email protected]>
Reviewed-by: David Dorwin <[email protected]>
Reviewed-by: Scott Violet <[email protected]>
Cr-Commit-Position: refs/heads/master@{#549073}
diff --git a/chrome/browser/flag_descriptions.h b/chrome/browser/flag_descriptions.h
index 85336dd..559ac28 100644
--- a/chrome/browser/flag_descriptions.h
+++ b/chrome/browser/flag_descriptions.h
@@ -1094,6 +1094,9 @@
 extern const char kWebXrName[];
 extern const char kWebXrDescription[];
 
+extern const char kWebXrHitTestName[];
+extern const char kWebXrHitTestDescription[];
+
 extern const char kWebXrOrientationSensorDeviceName[];
 extern const char kWebXrOrientationSensorDeviceDescription[];