Use autolayout in LocationBarView

Uses autolayout in LocationBarView to position the omnibox textfield.

Bug: 
Cq-Include-Trybots: master.tryserver.chromium.mac:ios-simulator-cronet
Change-Id: If9f0f9ec65624785617bb3820d56509845f97e5e
Reviewed-on: https://chromium-review.googlesource.com/709215
Commit-Queue: Stepan Khapugin <stkhapugin@chromium.org>
Reviewed-by: Rohit Rao (ping after 24h) <rohitrao@chromium.org>
Cr-Commit-Position: refs/heads/master@{#515911}

ios/chrome/browser/ui/omnibox/omnibox_text_field_ios.mm

@@ -110,14 +110,19 @@ NSString* const kOmniboxFadeAnimationKey = @"OmniboxFadeAnimation";
                                                   textColor:textColor
                                                   tintColor:tintColor];
     [self addSubview:_textField];
+
+    [NSLayoutConstraint activateConstraints:@[
+      [_textField.leftAnchor constraintEqualToAnchor:self.leftAnchor],
+      [_textField.rightAnchor constraintEqualToAnchor:self.rightAnchor],
+      [_textField.topAnchor constraintEqualToAnchor:self.topAnchor],
+      [_textField.bottomAnchor constraintEqualToAnchor:self.bottomAnchor],
+    ]];
+
+    _textField.translatesAutoresizingMaskIntoConstraints = NO;
   }
   return self;
 }
 
-- (void)layoutSubviews {
-  [super layoutSubviews];
-  self.textField.frame = self.bounds;
-}
 
 @end