Do not induce kCrashOnUnexpectedURLChange if previous hostname is empty.

URLDidChangeWithoutDocumentChange should not be called if previous
document hostname is empty. This state is a bug, but there is no value
in crashing.

TBR=eugenebut@google.com

(cherry picked from commit c984463)

Bug: 845933
Cq-Include-Trybots: luci.chromium.try:ios-simulator-full-configs;master.tryserver.chromium.mac:ios-simulator-cronet
Change-Id: I83ddc62ebc4211aa14f7819f8ea9a6d80d1b7e25
Reviewed-on: https://chromium-review.googlesource.com/1079368
Reviewed-by: Danyao Wang <danyao@chromium.org>
Reviewed-by: Rohit Rao <rohitrao@chromium.org>
Commit-Queue: Eugene But <eugenebut@chromium.org>
Cr-Original-Commit-Position: refs/heads/master@{#562941}
Reviewed-on: https://chromium-review.googlesource.com/1079816
Reviewed-by: Eugene But <eugenebut@chromium.org>
Cr-Commit-Position: refs/branch-heads/3440@{#50}
Cr-Branched-From: 010ddcf-refs/heads/master@{#561733}

ios/web/web_state/ui/crw_web_controller.mm

@@ -5273,12 +5273,14 @@ - (BOOL)isKVOChangePotentialSameDocumentNavigationToURL:(const GURL&)newURL {
 
 - (void)URLDidChangeWithoutDocumentChange:(const GURL&)newURL {
   DCHECK(newURL == net::GURLWithNSURL([_webView URL]));
+  DCHECK(!_documentURL.host().empty() || _documentURL.SchemeIsFile());
 
   if (base::FeatureList::IsEnabled(
           web::features::kCrashOnUnexpectedURLChange)) {
     if (_documentURL.GetOrigin() != newURL.GetOrigin()) {
-      if (newURL.username().find(_documentURL.host()) != std::string::npos ||
-          newURL.password().find(_documentURL.host()) != std::string::npos) {
+      if (!_documentURL.host().empty() &&
+          (newURL.username().find(_documentURL.host()) != std::string::npos ||
+           newURL.password().find(_documentURL.host()) != std::string::npos)) {
         CHECK(false);
       }
     }