Remove RenderViewHost parameter from WebContentsObserver::Did{Start|Stop}Loading.

chrome/browser/prerender/prerender_browsertest.cc

Index: chrome/browser/prerender/prerender_browsertest.cc
diff --git a/chrome/browser/prerender/prerender_browsertest.cc b/chrome/browser/prerender/prerender_browsertest.cc
index 290fb236a170f41845923d6e31760a873fc15513..0d3a86195150afd34f8cef1d289a06fb9365a479 100644
--- a/chrome/browser/prerender/prerender_browsertest.cc
+++ b/chrome/browser/prerender/prerender_browsertest.cc
@@ -311,10 +311,8 @@ class NavigationOrSwapObserver : public WebContentsObserver,
   }
 
   // WebContentsObserver implementation:
-  void DidStartLoading(RenderViewHost* render_view_host) override {
-    did_start_loading_ = true;
-  }
-  void DidStopLoading(RenderViewHost* render_view_host) override {
+  void DidStartLoading() override { did_start_loading_ = true; }
+  void DidStopLoading() override {
     if (!did_start_loading_)
       return;
     number_of_loads_--;