Do not ignore null navigation context on iOS 13

Workaround for null context was necessary on iOS 12
as confirmed by Navigation.IOSNullContextInDidFailProvisionalNavigation
histogram. Also stop recording Navigation.IOSNullContextInDidFailProvisionalNavigation
as this histogram has expired and served its purpose.

Bug: None
Change-Id: Id2df18c8e92c134049a820b6a38af403c38bac6d
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2638447
Commit-Queue: Eugene But <eugenebut@chromium.org>
Reviewed-by: Ali Juma <ajuma@chromium.org>
Reviewed-by: Brian White <bcwhite@chromium.org>
Reviewed-by: Gauthier Ambard <gambard@chromium.org>
Cr-Commit-Position: refs/heads/master@{#845902}

ios/web/navigation/crw_wk_navigation_handler.mm

@@ -5,6 +5,7 @@
 #import "ios/web/navigation/crw_wk_navigation_handler.h"
 
 #include "base/feature_list.h"
+#include "base/ios/ios_util.h"
 #import "base/ios/ns_error_util.h"
 #include "base/metrics/histogram_functions.h"
 #include "base/metrics/histogram_macros.h"
@@ -1817,11 +1818,8 @@ void ReportOutOfSyncURLInDidStartProvisionalNavigation(
         web::RequiresProvisionalNavigationFailureWorkaround()) {
       // It is likely that |navigationContext| is null because
       // didStartProvisionalNavigation: was not called with this WKNavigation
-      // object. Log UMA to know when this workaround can be removed and
-      // do not call OnNavigationFinished() to avoid crash on null pointer
-      // dereferencing. See crbug.com/973653 and crbug.com/1004634 for details.
-      UMA_HISTOGRAM_BOOLEAN(
-          "Navigation.IOSNullContextInDidFailProvisionalNavigation", true);
+      // object, which was pretty common on iOS 12 and fixed on iOS 13.
+      // See crbug.com/973653 and crbug.com/1004634 for details.
       return;
     }
   }
@@ -2059,16 +2057,10 @@ void ReportOutOfSyncURLInDidStartProvisionalNavigation(
     }
 
     if (provisionalLoad) {
-      if (!navigationContext &&
-          web::RequiresProvisionalNavigationFailureWorkaround()) {
+      if (base::ios::IsRunningOnIOS13OrLater() || navigationContext) {
         // It is likely that |navigationContext| is null because
         // didStartProvisionalNavigation: was not called with this WKNavigation
-        // object. Log UMA to know when this workaround can be removed and
-        // do not call OnNavigationFinished() to avoid crash on null pointer
-        // dereferencing. See crbug.com/973653 for details.
-        UMA_HISTOGRAM_BOOLEAN(
-            "Navigation.IOSNullContextInDidFailProvisionalNavigation", true);
-      } else {
+        // object. See crbug.com/973653 for details.
         self.webStateImpl->OnNavigationFinished(navigationContext.get());
       }
     }

tools/metrics/histograms/histograms_xml/navigation/histograms.xml

@@ -671,8 +671,11 @@ reviews. Googlers can read more about this at go/gwsq-gerrit.
 
 <histogram name="Navigation.IOSNullContextInDidFailProvisionalNavigation"
     enum="Boolean" expires_after="M85">
+  <obsolete>
+    Removed from code in Jan 2021.
+  </obsolete>
   <owner>ajuma@chromium.org</owner>
-  <owner>eugenebut@chromium.org</owner>
+  <owner>gambard@chromium.org</owner>
   <summary>
     Logged when NavigationContext is null inside -[WKNavigationDelegate
     webView:didFailProvisionalNavigation]. If Chrome stopped logging this metric