[ios] Active web state observer in tab collection.

ios/clean/chrome/browser/ui/tab_collection/tab_collection_tab_cell.mm

 // Copyright 2016 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/clean/chrome/browser/ui/tab_collection/tab_collection_tab_cell.h"
 
 #if !defined(__has_feature) || !__has_feature(objc_arc)
 #error "This file requires ARC support."
 #endif
 
 namespace {
+const CGFloat kBorderMargin = 6.0f;
 const CGFloat kSelectedBorderCornerRadius = 8.0f;
 const CGFloat kSelectedBorderWidth = 4.0f;
 }
 
 @implementation TabCollectionTabCell
 
 - (instancetype)initWithFrame:(CGRect)frame {
   if ((self = [super initWithFrame:frame])) {
-    self.selectedBackgroundView = [[UIView alloc] init];
-    self.selectedBackgroundView.backgroundColor = [UIColor blackColor];
-    self.selectedBackgroundView.layer.cornerRadius =
-        kSelectedBorderCornerRadius;
-    self.selectedBackgroundView.layer.borderWidth = kSelectedBorderWidth;
-    self.selectedBackgroundView.layer.borderColor = self.tintColor.CGColor;
-    self.selectedBackgroundView.transform = CGAffineTransformScale(
-        self.selectedBackgroundView.transform, 1.08, 1.08);
+    [self setupSelectedBackgroundView];
   }
   return self;
 }
 
+- (void)setupSelectedBackgroundView {

[marq (ping after 24h), 2017/05/30 11:09:43]

This is fine for this CL, but consider getting in the habit of keeping the
changes in each CL logically grouped. This fix is small and would have landed
quickly as an independent CL.

[edchin, 2017/06/01 23:52:28]

Acknowledged.

+  self.selectedBackgroundView = [[UIView alloc] init];
+  self.selectedBackgroundView.backgroundColor = [UIColor blackColor];
+
+  UIView* border = [[UIView alloc] init];
+  border.translatesAutoresizingMaskIntoConstraints = NO;
+  border.backgroundColor = [UIColor blackColor];
+  border.layer.cornerRadius = kSelectedBorderCornerRadius;
+  border.layer.borderWidth = kSelectedBorderWidth;
+  border.layer.borderColor = self.tintColor.CGColor;
+  [self.selectedBackgroundView addSubview:border];
+  [NSLayoutConstraint activateConstraints:@[
+    [border.topAnchor
+        constraintEqualToAnchor:self.selectedBackgroundView.topAnchor
+                       constant:-kBorderMargin],
+    [border.leadingAnchor
+        constraintEqualToAnchor:self.selectedBackgroundView.leadingAnchor
+                       constant:-kBorderMargin],
+    [border.trailingAnchor
+        constraintEqualToAnchor:self.selectedBackgroundView.trailingAnchor
+                       constant:kBorderMargin],
+    [border.bottomAnchor
+        constraintEqualToAnchor:self.selectedBackgroundView.bottomAnchor
+                       constant:kBorderMargin]
+  ]];
+}
+
 @end