Add experiment for having a "Beta forum" link in the help menu.

chrome/common/url_constants.cc

Index: chrome/common/url_constants.cc
diff --git a/chrome/common/url_constants.cc b/chrome/common/url_constants.cc
index f620dc446cc2c98126870276b405f8e180d36bbf..de425a2144d191711c5f33078b1cbaa32d0b5bb6 100644
--- a/chrome/common/url_constants.cc
+++ b/chrome/common/url_constants.cc
@@ -451,6 +451,9 @@ const char kChromeHelpViaWebUIURL[] =
     "https://support.google.com/chrome/?p=help&ctx=settings";
 #endif  // defined(OS_CHROMEOS)
 
+const char kChromeBetaForumURL[] =
+    "https://support.google.com/chrome/?p=beta_forum";
+
 #if defined(OS_CHROMEOS)
 const char kChromeAccessibilityHelpURL[] =
     "https://support.google.com/chromebook/topic/6323347";