Add some UMA for recent tabs

chrome/browser/android/offline_pages/recent_tab_helper.cc

Index: chrome/browser/android/offline_pages/recent_tab_helper.cc
diff --git a/chrome/browser/android/offline_pages/recent_tab_helper.cc b/chrome/browser/android/offline_pages/recent_tab_helper.cc
index 6f5fc9b3aa3fa722ad8772020c4f17e94b469871..5aa73eeb76c954bab55ecfa7a27d64a7a5742192 100644
--- a/chrome/browser/android/offline_pages/recent_tab_helper.cc
+++ b/chrome/browser/android/offline_pages/recent_tab_helper.cc
@@ -11,6 +11,7 @@
 #include "base/location.h"
 #include "base/logging.h"
 #include "base/macros.h"
+#include "base/metrics/histogram_macros.h"
 #include "base/thread_task_runner_handle.h"
 #include "base/time/time.h"
 #include "chrome/browser/android/offline_pages/offline_page_mhtml_archiver.h"
@@ -92,7 +93,7 @@ void RecentTabHelper::StartSnapshot() {
 
   GURL url = web_contents()->GetLastCommittedURL();
   if (!page_model_->CanSavePage(url)) {
-    // TODO(dimich): Add UMA. Bug 608112.
+    UMA_HISTOGRAM_BOOLEAN("OfflinePages.CanNotSaveRecentPage", true);

[fgorski, 2016/05/11 19:34:39]

ok, I guess this is turning into a SQL patch after all.

I think boolean histogram is the right choice, but I also think you should
report it outside (before) you hit the if. That way you will compare can save
vs. cannot save.

The way the code is written now, we only ever report true. (and yes, the counts
are better for that)

[bburns, 2016/05/11 19:43:01]

Done.

     return;
   }
 
@@ -180,7 +181,6 @@ void RecentTabHelper::ContinueSnapshotAfterPurge(
 
 void RecentTabHelper::SavePageCallback(OfflinePageModel::SavePageResult result,
                                        int64_t offline_id) {
-  // TODO(dimich): add UMA, including result. Bug 608112.
   ReportSnapshotCompleted();
 }