Remove NavigationRequestInfo::is_showing.

Trying to initialize it causes content_shell --enable-browser-side-navigation
to crash on startup.

It corresponds to ResourceRequestInfo::GetVisibilityState, but that's only used
for categorizing requests made from prerender which needs a different bit
(WebPageVisiblityStatePrerender vs. others), so we'll need to revisit it
anyway.

BUG=376014

Review URL: https://codereview.chromium.org/534393002

Cr-Commit-Position: refs/heads/master@{#293211}

content/browser/frame_host/navigation_request_info.cc

@@ -12,8 +12,7 @@ NavigationRequestInfo::NavigationRequestInfo(
     const FrameHostMsg_BeginNavigation_Params& params)
     : navigation_params(params),
       is_main_frame(true),
-      parent_is_main_frame(false),
-      is_showing(true) {
+      parent_is_main_frame(false) {
 }
 
 }  // namespace content

content/browser/frame_host/navigation_request_info.h

@@ -32,9 +32,6 @@ struct NavigationRequestInfo {
   GURL first_party_for_cookies;
   bool is_main_frame;
   bool parent_is_main_frame;
-
-  // True if the frame is visible.
-  bool is_showing;
 };
 
 }  // namespace content

content/browser/frame_host/render_frame_host_manager.cc

@@ -577,7 +577,6 @@ void RenderFrameHostManager::OnBeginNavigation(
   info.is_main_frame = frame_tree_node_->IsMainFrame();
   info.parent_is_main_frame = !frame_tree_node_->parent() ?
       false : frame_tree_node_->parent()->IsMainFrame();
-  info.is_showing = GetRenderWidgetHostView()->IsShowing();
 
   // TODO(clamy): Check if the current RFH should be initialized (in case it has
   // crashed) not to display a sad tab while navigating.