Remove RenderFrameHostManager::current_host()

This is just a small cleanup to remove this RenderViewHost getter,
since it's confusingly named (given the presence of
current_frame_host()).  The RenderViewHost can instead be retrieved
directly from RenderFrameHost.

This exposed one tricky corner case, which relied on a null check for
current_frame_host() in current_host().  That case has been fixed in
WebContentsImpl::RenderViewTerminated().

Bug: 1015882
Change-Id: I0288c716913d11620bfe949c2da8d6e0683e57b8
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2654478
Commit-Queue: Alex Moshchuk <[email protected]>
Reviewed-by: Charlie Reis <[email protected]>
Cr-Commit-Position: refs/heads/master@{#849994}
diff --git a/content/browser/renderer_host/navigation_controller_impl.cc b/content/browser/renderer_host/navigation_controller_impl.cc
index c5abb179..bcd5fc4 100644
--- a/content/browser/renderer_host/navigation_controller_impl.cc
+++ b/content/browser/renderer_host/navigation_controller_impl.cc
@@ -813,8 +813,8 @@
 
 bool NavigationControllerImpl::CanViewSource() {
   const std::string& mime_type = frame_tree_.root()
-                                     ->render_manager()
-                                     ->current_host()
+                                     ->current_frame_host()
+                                     ->render_view_host()
                                      ->contents_mime_type();
   bool is_viewable_mime_type = blink::IsSupportedNonImageMimeType(mime_type) &&
                                !media::IsSupportedMediaMimeType(mime_type);