VR: Dynamically load GVR Keyboard implementation

This CL add the necessary glue to wire up the keyboard API to its
implementation in the Daydream Keyboard APK.

The keyboard can be temporarily be summoned via the app button by
turning on the vr-browser-keyboard runtime flag. Follow-up CLs will
introduce the keyboard element and remove the temporary code in
VrShellGl.

Bug: 641470
Change-Id: I3d1372aa335db69c1e38adbb00a67993f9eea1e0
Reviewed-on: https://chromium-review.googlesource.com/731568
Commit-Queue: Yash Malik <[email protected]>
Reviewed-by: Yaron Friedman <[email protected]>
Reviewed-by: Biao She <[email protected]>
Reviewed-by: Amirhossein Simjour <[email protected]>
Reviewed-by: Max Moroz <[email protected]>
Reviewed-by: Ian Vollick <[email protected]>
Cr-Commit-Position: refs/heads/master@{#517638}
diff --git a/chrome/browser/flag_descriptions.h b/chrome/browser/flag_descriptions.h
index 1850a7b0..135b31d5 100644
--- a/chrome/browser/flag_descriptions.h
+++ b/chrome/browser/flag_descriptions.h
@@ -1679,6 +1679,9 @@
 extern const char kVrBrowsingName[];
 extern const char kVrBrowsingDescription[];
 
+extern const char kVrBrowserKeyboardName[];
+extern const char kVrBrowserKeyboardDescription[];
+
 extern const char kVrBrowsingExperimentalFeaturesName[];
 extern const char kVrBrowsingExperimentalFeaturesDescription[];