Do not create CRWWebUIManager for non-WebUI URLs.

ios/web/web_state/ui/crw_web_controller.mm

 // Copyright 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #import "ios/web/web_state/ui/crw_web_controller.h"
 
 #import <WebKit/WebKit.h>
 
 #import <objc/runtime.h>
 #include <stddef.h>
@@ skipping 3144 matching lines @@
   // Don't cancel NSURLErrorCancelled errors originating from navigation
   // as the WKWebView will automatically retry these loads.
   WKWebViewErrorSource source = WKWebViewErrorSourceFromError(error);
   return source != NAVIGATION;
 }
 
 #pragma mark -
 #pragma mark WebUI
 
 - (void)createWebUIForURL:(const GURL&)URL {
   _webStateImpl->CreateWebUI(URL);

[PL, 2017/05/17 00:04:26]

For chrome://crash we would still run CreateWebUI even though we weren't
creating a web UI, is that a problem?

[Eugene But (OOO till 7-30), 2017/05/17 14:49:26]

That should not be a problem. Added explanation comment to the code:
"|CreateWebUI| will do nothing if |URL| is not a WebUI URL.". 

-  _webUIManager.reset(
-      [[CRWWebUIManager alloc] initWithWebState:self.webStateImpl]);
+  bool isWebUIURL = _webStateImpl->HasWebUI();
+  if (isWebUIURL) {
+    _webUIManager.reset(
+        [[CRWWebUIManager alloc] initWithWebState:_webStateImpl]);
+  }
 }
 
 - (void)clearWebUI {
   _webStateImpl->ClearWebUI();
   _webUIManager.reset();
 }
 
 #pragma mark -
 #pragma mark Auth Challenge
 
@@ skipping 933 matching lines @@
           messageRouter:messageRouter
       completionHandler:^(NSError* loadError) {
         if (loadError)
           [self handleLoadError:loadError inMainFrame:YES forNavigation:nil];
         else
           self.webStateImpl->SetContentsMimeType("text/html");
       }];
 }
 
 - (void)loadHTML:(NSString*)HTML forURL:(const GURL&)URL {
+  DCHECK(HTML.length);
   // Remove the transient content view.
   [self clearTransientContentView];
 
   _loadPhase = web::LOAD_REQUESTED;
 
   // Web View should not be created for App Specific URLs.
   if (!web::GetWebClient()->IsAppSpecificURL(URL)) {
     [self ensureWebViewCreated];
     DCHECK(_webView) << "_webView null while trying to load HTML";
   }
@@ skipping 1033 matching lines @@
 - (NSUInteger)observerCount {
   DCHECK_EQ(_observerBridges.size(), [_observers count]);
   return [_observers count];
 }
 
 - (NSString*)referrerFromNavigationAction:(WKNavigationAction*)action {
   return [action.request valueForHTTPHeaderField:kReferrerHeaderName];
 }
 
 @end