Add support to previews/ for Server LoFi and LitePages

components/previews/core/previews_black_list.cc

Index: components/previews/core/previews_black_list.cc
diff --git a/components/previews/core/previews_black_list.cc b/components/previews/core/previews_black_list.cc
index ea5de7d822f6ebb8cf9d5504a500ad896895303a..ffd35cc71e52cb52aabdb3ac76e0befdec502f10 100644
--- a/components/previews/core/previews_black_list.cc
+++ b/components/previews/core/previews_black_list.cc
@@ -6,7 +6,7 @@
 
 #include "base/bind.h"
 #include "base/memory/ptr_util.h"
-#include "base/metrics/histogram_macros.h"
+#include "base/metrics/histogram.h"
 #include "base/optional.h"
 #include "base/time/clock.h"
 #include "components/previews/core/previews_black_list_item.h"
@@ -74,13 +74,12 @@ void PreviewsBlackList::AddPreviewNavigation(const GURL& url,
                                              PreviewsType type) {
   DCHECK(thread_checker_.CalledOnValidThread());
   DCHECK(url.has_host());
-  switch (type) {
-    case PreviewsType::OFFLINE:
-      UMA_HISTOGRAM_BOOLEAN("Previews.OptOut.UserOptedOut.Offline", opt_out);
-      break;
-    default:
-      NOTREACHED();
-  }
+  std::string histogram_name("Previews.OptOut.UserOptedOut.");

[tbansal1, 2017/05/02 21:49:31]

Use StringPiece or   base::StringPrintf to reduce overhead of string
manipulation.

[RyanSturm, 2017/05/02 22:57:18]

Done.

+  histogram_name.append(GetStringNameForType(type));
+
+  base::BooleanHistogram::FactoryGet(
+      histogram_name, base::HistogramBase::kUmaTargetedHistogramFlag)
+      ->Add(opt_out);
   if (opt_out) {
     last_opt_out_time_ = clock_->Now();
   }