Skip CRWGenericContentView layout if the bounds size hasn't changed.

ios/web/web_state/ui/crw_generic_content_view.mm

 // Copyright 2015 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/public/web_state/ui/crw_generic_content_view.h"
 
 #include "base/logging.h"
 #include "base/mac/scoped_nsobject.h"
 
 @interface CRWGenericContentView () {
+  // The size of the view's bounds at the last call to |-layoutSubviews|.
+  CGSize _lastLayoutSize;
   // Backing objectect for |self.scrollView|.
   base::scoped_nsobject<UIScrollView> _scrollView;
   // Backing object for |self.view|.
   base::scoped_nsobject<UIView> _view;
 }
 
 @end
 
 @implementation CRWGenericContentView
 
 - (instancetype)initWithView:(UIView*)view {
   self = [super initWithFrame:CGRectZero];
   if (self) {
     DCHECK(view);
+    _lastLayoutSize = CGSizeZero;
     _view.reset([view retain]);
     _scrollView.reset([[UIScrollView alloc] initWithFrame:CGRectZero]);
     [self addSubview:_scrollView];
     [_scrollView addSubview:_view];
     [_scrollView setBackgroundColor:[_view backgroundColor]];
   }
   return self;
 }
 
 - (instancetype)initWithCoder:(NSCoder*)decoder {
@@ skipping 17 matching lines @@
 
 - (UIView*)view {
   return _view.get();
 }
 
 #pragma mark Layout
 
 - (void)layoutSubviews {
   [super layoutSubviews];
 
+  // Early return if the bounds' size hasn't changed since the last layout.
+  if (CGSizeEqualToSize(_lastLayoutSize, self.bounds.size))
+    return;
+  _lastLayoutSize = self.bounds.size;
+
   // scrollView layout.
   self.scrollView.frame = self.bounds;
 
   // view layout.
   CGRect contentRect =
       UIEdgeInsetsInsetRect(self.bounds, self.scrollView.contentInset);
   CGSize viewSize = [self.view sizeThatFits:contentRect.size];
   self.view.frame = CGRectMake(0.0, 0.0, viewSize.width, viewSize.height);
 
   // UIScrollViews only scroll vertically if the content size's height is
-  // creater than that of its content rect.
+  // greater than that of its content rect.
   if (viewSize.height <= CGRectGetHeight(contentRect)) {
     CGFloat singlePixel = 1.0f / [[UIScreen mainScreen] scale];
     viewSize.height = CGRectGetHeight(contentRect) + singlePixel;
   }
   self.scrollView.contentSize = viewSize;
 }
 
 - (BOOL)isViewAlive {
   return YES;
 }
 
 @end