Stop triggering context menu while scrolling

ios/web/web_state/ui/crw_context_menu_controller.mm

 // Copyright 2017 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_context_menu_controller.h"
 
 #import <objc/runtime.h>
 #include <stddef.h>
 
 #import "base/ios/weak_nsobject.h"
@@ skipping 285 matching lines @@
   [self fetchDOMElementAtPoint:[touch locationInView:_webView]
              completionHandler:^(NSDictionary* element) {
                [weakSelf setDOMElementForLastTouch:element];
              }];
   return YES;
 }
 
 - (BOOL)gestureRecognizerShouldBegin:(UIGestureRecognizer*)gestureRecognizer {
   // Expect only _contextMenuRecognizer.
   DCHECK([gestureRecognizer isEqual:_contextMenuRecognizer]);
+
+  // Context menu should not be triggered while scrolling, as some users tend to
+  // stop scrolling by resting the finger on the screen instead of touching the
+  // screen. For more info, please refer to crbug.com/642375.
+  if ([self webScrollView].dragging) {
+    return NO;
+  }
+
   // Fetching is considered as successful even if |_DOMElementForLastTouch| is
   // empty. However if |_DOMElementForLastTouch| is empty then custom context
   // menu should not be shown.
   UMA_HISTOGRAM_BOOLEAN("WebController.FetchContextMenuInfoAsyncSucceeded",
                         !!_DOMElementForLastTouch);
   return [_DOMElementForLastTouch count];
 }
 
 #pragma mark -
 #pragma mark Web Page Features
@@ skipping 21 matching lines @@
         [NSString stringWithFormat:@"__gCrWeb.getElementFromPoint(%g, %g);",
                                    localPoint.x, localPoint.y];
     [self executeJavaScript:kGetElementScript
           completionHandler:^(id element, NSError*) {
             handler(base::mac::ObjCCastStrict<NSDictionary>(element));
           }];
   }];
 }
 
 @end