PlzNavigate: Add tests to check WebUI navigations.

content/browser/frame_host/render_frame_host_manager.cc

Index: content/browser/frame_host/render_frame_host_manager.cc
diff --git a/content/browser/frame_host/render_frame_host_manager.cc b/content/browser/frame_host/render_frame_host_manager.cc
index 612868ecc20d6f8dde95c092e9849d5acc81b5fd..bfbe454ae480690315739f8660d59b4e8b79252b 100644
--- a/content/browser/frame_host/render_frame_host_manager.cc
+++ b/content/browser/frame_host/render_frame_host_manager.cc
@@ -1000,7 +1000,10 @@ RenderFrameHostImpl* RenderFrameHostManager::GetFrameHostForNavigation(
     // Reuse the current RFH if its SiteInstance matches the the navigation's
     // or if this is a subframe navigation. We only swap RFHs for subframes when
     // --site-per-process is enabled.
-    CleanUpNavigation();
+
+    if (speculative_render_frame_host_)
+      DiscardUnusedFrame(UnsetSpeculativeRenderFrameHost());
+
     navigation_rfh = render_frame_host_.get();
 
     // As SiteInstances are the same, make the RFH update its possible pending
@@ -1092,8 +1095,6 @@ RenderFrameHostImpl* RenderFrameHostManager::GetFrameHostForNavigation(
 void RenderFrameHostManager::CleanUpNavigation() {
   CHECK(base::CommandLine::ForCurrentProcess()->HasSwitch(
       switches::kEnableBrowserSideNavigation));
-  // TODO(carlosk): the discarding of the current RFH WebUI and the cleanup of
-  // the speculative RFH should not always happen together.
   render_frame_host_->DiscardPendingWebUI();
   if (speculative_render_frame_host_)
     DiscardUnusedFrame(UnsetSpeculativeRenderFrameHost());