[Offline Pages] Adds Rappor metrics measuring what domains are saved & viewed.

chrome/browser/android/offline_pages/offline_page_tab_helper.cc

Index: chrome/browser/android/offline_pages/offline_page_tab_helper.cc
diff --git a/chrome/browser/android/offline_pages/offline_page_tab_helper.cc b/chrome/browser/android/offline_pages/offline_page_tab_helper.cc
index 3d064bdb51451a42f92d9653bf238c7aa8f20978..6f43b9f55c2dc9dfd29842672c62fa0f8f68c5eb 100644
--- a/chrome/browser/android/offline_pages/offline_page_tab_helper.cc
+++ b/chrome/browser/android/offline_pages/offline_page_tab_helper.cc
@@ -9,6 +9,8 @@
 #include "base/metrics/histogram.h"
 #include "base/threading/thread_task_runner_handle.h"
 #include "chrome/browser/android/offline_pages/offline_page_utils.h"
+#include "chrome/browser/browser_process.h"
+#include "components/rappor/rappor_utils.h"
 #include "content/public/browser/browser_thread.h"
 #include "content/public/browser/navigation_controller.h"
 #include "content/public/browser/navigation_entry.h"
@@ -107,16 +109,22 @@ void OfflinePageTabHelper::DidFinishNavigation(
     return;
   }
 
+  GURL online_url = navigation_handle->GetURL();
+
   // When the navigation starts, we redirect immediately from online page to
   // offline version on the case that there is no network connection. If there
   // is still network connection but with no or poor network connectivity, the
   // navigation will eventually fail and we want to redirect to offline copy
   // in this case.
   GURL offline_url = offline_pages::OfflinePageUtils::GetOfflineURLForOnlineURL(
-      web_contents()->GetBrowserContext(), navigation_handle->GetURL());
+      web_contents()->GetBrowserContext(), online_url);
   if (!offline_url.is_valid())
     return;
 
+  rappor::SampleDomainAndRegistryFromGURL(
+      g_browser_process->rappor_service(),
+      "OfflinePages.OfflineVersionWasViewedWhileOffline", online_url);
+
   base::ThreadTaskRunnerHandle::Get()->PostTask(
       FROM_HERE,
       base::Bind(&OfflinePageTabHelper::Redirect,