Use consistent background color for WKWebViews.

ios/web/web_state/web_view_internal_creation_util.mm

 // Copyright 2014 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/web_view_internal_creation_util.h"
 
 #import <objc/runtime.h>
 #import <WebKit/WebKit.h>
 
 #include "base/logging.h"
@@ skipping 23 matching lines @@
 namespace {
 // Returns the counter of all the active WKWebViews.
 // DEPRECATED. Please use web::WebViewCounter instead.
 // TODO(shreyasv): Remove this once all callers have stopped using it.
 // crbug.com/480507
 web::WeakNSObjectCounter& GetActiveWKWebViewCounter() {
   static web::WeakNSObjectCounter active_wk_web_view_counter;
   return active_wk_web_view_counter;
 }
 
+// The brightness of the web views' background colors.
+const CGFloat kWebViewBackgroundColorBrightness = 0.2;
+
 // Decides if web views can be created.
 bool gAllowWebViewCreation = NO;
 
 // Decides if web views are associated with an ActiveStateManager which is
 // active.
 bool gWebViewsNeedActiveStateManager = NO;
 
 }  // namespace
 
 @interface WKWebView (CRWAdditions)
@@ skipping 123 matching lines @@
                            BrowserState* browser_state) {
   VerifyWKWebViewCreationPreConditions(browser_state, configuration);
 
   PreWKWebViewCreation(browser_state);
 #if !defined(NDEBUG)
   bool previous_allow_web_view_creation_value = gAllowWebViewCreation;
   gAllowWebViewCreation = true;
 #endif
   WKWebView* result =
       [[WKWebView alloc] initWithFrame:frame configuration:configuration];
+  result.backgroundColor =
+      [UIColor colorWithWhite:kWebViewBackgroundColorBrightness alpha:1.0];
 #if !defined(NDEBUG)
   gAllowWebViewCreation = previous_allow_web_view_creation_value;
 #endif
   PostWKWebViewCreation(result, browser_state);
 
   // By default the web view uses a very sluggish scroll speed. Set it to a more
   // reasonable value.
   result.scrollView.decelerationRate = UIScrollViewDecelerationRateNormal;
 
   return result;
@@ skipping 67 matching lines @@
     if (!gAllowWebViewCreation) {
       gWebViewsNeedActiveStateManager =
           GetWebClient()->WebViewsNeedActiveStateManager();
     }
   });
   return gAllowWebViewCreation;
 }
 #endif
 
 }  // namespace web