Add unit test for WebRTCInternalsMessageHandler.

content/browser/media/webrtc/webrtc_internals_message_handler.h

Index: content/browser/media/webrtc/webrtc_internals_message_handler.h
diff --git a/content/browser/media/webrtc/webrtc_internals_message_handler.h b/content/browser/media/webrtc/webrtc_internals_message_handler.h
index 82e242eea9d322187e66f6d77d6f7f757bc63c91..296ada15280b14dfa01996298c2b378a536629ad 100644
--- a/content/browser/media/webrtc/webrtc_internals_message_handler.h
+++ b/content/browser/media/webrtc/webrtc_internals_message_handler.h
@@ -17,11 +17,13 @@ class ListValue;
 namespace content {
 
 class RenderFrameHost;
+class WebRTCInternals;
 
 // This class handles messages to and from WebRTCInternalsUI.
 // It delegates all its work to WebRTCInternalsProxy on the IO thread.
-class WebRTCInternalsMessageHandler : public WebUIMessageHandler,
-                                      public WebRTCInternalsUIObserver{
+class CONTENT_EXPORT WebRTCInternalsMessageHandler
+    : public WebUIMessageHandler,
+      public NON_EXPORTED_BASE(WebRTCInternalsUIObserver) {
  public:
   WebRTCInternalsMessageHandler();
   ~WebRTCInternalsMessageHandler() override;
@@ -32,6 +34,12 @@ class WebRTCInternalsMessageHandler : public WebUIMessageHandler,
   // WebRTCInternalsUIObserver override.
   void OnUpdate(const std::string& command, const base::Value* args) override;
 
+ protected:
+  // The WebRTCInternals to use. Always WebRTCInternals::GetInstance()
+  // except for testing.
+  explicit WebRTCInternalsMessageHandler(WebRTCInternals* webrtc_internals);
+  WebRTCInternals* const webrtc_internals_;
+
  private:
   // Returns a pointer to the RFH iff it is currently hosting the
   // webrtc-internals page.