Eliminate extra Native->JS->Native roundrip when showing context menu.

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>
 
 #include "base/logging.h"
@@ skipping 40 matching lines @@
 // The scroll view of |webView|.
 @property(nonatomic, readonly, weak) id<CRWContextMenuDelegate> delegate;
 // Returns the x, y offset the content has been scrolled.
 @property(nonatomic, readonly) CGPoint scrollPosition;
 
 // Called when the window has determined there was a long-press and context menu
 // must be shown.
 - (void)showContextMenu:(UIGestureRecognizer*)gestureRecognizer;
 // Cancels all touch events in the web view (long presses, tapping, scrolling).
 - (void)cancelAllTouches;
-// Asynchronously fetches full width of the rendered web page.
-- (void)fetchWebPageWidthWithCompletionHandler:(void (^)(CGFloat))handler;
 // Asynchronously fetches information about DOM element for the given point (in
 // UIView coordinates). |handler| can not be nil. See |_DOMElementForLastTouch|
 // for element format description.
 - (void)fetchDOMElementAtPoint:(CGPoint)point
              completionHandler:(void (^)(NSDictionary*))handler;
 // Sets the value of |_DOMElementForLastTouch|.
 - (void)setDOMElementForLastTouch:(NSDictionary*)element;
 // Forwards the execution of |script| to |javaScriptDelegate| and if it is nil,
 // to |webView|.
 - (void)executeJavaScript:(NSString*)script
@@ skipping 145 matching lines @@
   // 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
 
-- (void)fetchWebPageWidthWithCompletionHandler:(void (^)(CGFloat))handler {
-  [self executeJavaScript:@"__gCrWeb.getPageWidth();"
-        completionHandler:^(id pageWidth, NSError*) {
-          handler([base::mac::ObjCCastStrict<NSNumber>(pageWidth) floatValue]);
-        }];
-}
-
 - (void)fetchDOMElementAtPoint:(CGPoint)point
              completionHandler:(void (^)(NSDictionary*))handler {
   DCHECK(handler);
-  // Convert point into web page's coordinate system (which may be scaled and/or
-  // scrolled).
   CGPoint scrollOffset = self.scrollPosition;
-  CGFloat webViewContentWidth = self.webScrollView.contentSize.width;
-  CRWContextMenuController* weakSelf = self;
-  [self fetchWebPageWidthWithCompletionHandler:^(CGFloat pageWidth) {
-    CGFloat scale = pageWidth / webViewContentWidth;
-    CGPoint localPoint = CGPointMake((point.x + scrollOffset.x) * scale,
-                                     (point.y + scrollOffset.y) * scale);
-    NSString* const kGetElementScript =
-        [NSString stringWithFormat:@"__gCrWeb.getElementFromPoint(%g, %g);",
-                                   localPoint.x, localPoint.y];
-    [weakSelf executeJavaScript:kGetElementScript
-              completionHandler:^(id element, NSError*) {
-                handler(base::mac::ObjCCastStrict<NSDictionary>(element));
-              }];
-  }];
+  CGSize webViewContentSize = self.webScrollView.contentSize;
+  CGFloat webViewContentWidth = webViewContentSize.width;
+  CGFloat webViewContentHeight = webViewContentSize.height;
+  NSString* getElementScript = [NSString
+      stringWithFormat:@"__gCrWeb.getElementFromPoint(%g, %g, %g, %g);",
+                       point.x + scrollOffset.x, point.y + scrollOffset.y,
+                       webViewContentWidth, webViewContentHeight];
+  [self executeJavaScript:getElementScript
+        completionHandler:^(id element, NSError*) {
+          handler(base::mac::ObjCCastStrict<NSDictionary>(element));
+        }];
 }
 
 @end