Add chrome://interstitials link to chrome://chrome-urls

Bug: 875623
Change-Id: I746ddd20e991615f875ca479aab4abca921f123c
Reviewed-on: https://chromium-review.googlesource.com/1181659Reviewed-by: Tommy Li <tommycli@chromium.org>
Commit-Queue: Mustafa Emre Acer <meacer@chromium.org>
Cr-Commit-Position: refs/heads/master@{#584548}

chrome/common/webui_url_constants.cc

@@ -324,6 +324,7 @@ const char* const kChromeHostURLs[] = {
     kChromeUIFlagsHost,
     kChromeUIGCMInternalsHost,
     kChromeUIHistoryHost,
+    kChromeUIInterstitialHost,
     kChromeUIInterventionsInternalsHost,
     kChromeUIInvalidationsHost,
     kChromeUILocalStateHost,