Change WebRTC SslCipher to be exposed as number only.

talk/app/webrtc/fakemetricsobserver.h

Index: talk/app/webrtc/fakemetricsobserver.h
diff --git a/talk/app/webrtc/fakemetricsobserver.h b/talk/app/webrtc/fakemetricsobserver.h
index 39454bf4db48862a32b0b7d7b64ed6a1bc184502..2b08230662c5b01c727dc0792f871127956adf42 100644
--- a/talk/app/webrtc/fakemetricsobserver.h
+++ b/talk/app/webrtc/fakemetricsobserver.h
@@ -46,25 +46,21 @@ class FakeMetricsObserver : public MetricsObserverInterface {
                             int counter_max) override;
   void AddHistogramSample(PeerConnectionMetricsName type,
                           int value) override;
-  void AddHistogramSample(PeerConnectionMetricsName type,
-                          const std::string& value) override;
 
   // Accessors to be used by the tests.
   int GetEnumCounter(PeerConnectionEnumCounterType type, int counter) const;
-  int GetIntHistogramSample(PeerConnectionMetricsName type) const;
-  const std::string& GetStringHistogramSample(
-      PeerConnectionMetricsName type) const;
+  int GetHistogramSample(PeerConnectionMetricsName type) const;
 
  protected:
   ~FakeMetricsObserver() {}
 
  private:
   rtc::ThreadChecker thread_checker_;
-  // This is a 2 dimension array. The first index is the enum counter type. The
-  // 2nd index is the counter of that particular enum counter type.
-  std::vector<std::vector<int>> counters_;
-  int int_histogram_samples_[kPeerConnectionMetricsName_Max];
-  std::string string_histogram_samples_[kPeerConnectionMetricsName_Max];
+  // The vector contains maps for each counter type. In the map, it's a mapping
+  // from individual counter to its count, such that it's memory efficient when
+  // comes to sparse enum type, like SSL cipher IANA registry.
+  std::vector<std::map<int, int>> counters_;
+  int histogram_samples_[kPeerConnectionMetricsName_Max];
 };
 
 }  // namespace webrtc