[ios] Adds LocationBarCoordinator.

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

 // Copyright (c) 2012 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.
 
 #include "ios/chrome/browser/ui/omnibox/omnibox_view_ios.h"
 
 #import <CoreText/CoreText.h>
 #import <MobileCoreServices/MobileCoreServices.h>
 
 #include "base/auto_reset.h"
@@ skipping 148 matching lines @@
 - (void)willPaste {
   editView_->WillPaste();
 }
 
 - (void)onDeleteBackward {
   editView_->OnDeleteBackward();
 }
 
 @end
 
 OmniboxViewIOS::OmniboxViewIOS(OmniboxTextFieldIOS* field,

[rohitrao (ping after 24h), 2017/04/05 13:36:14]

Mark and I chatted in person about this design.  I'm going to try and wrap the
OmniboxTextFieldIOS in two protocols: one that's a write-only consumer
interface, and a second that's a read-only datasource interface.

The LocationBarController and OmniboxViewIOS will get pointers to these two
protocols instead of getting a pointer to the text field directly.  That should
let us keep the text field encapsulated within the VC (instead the VC will
implement these protocols and forward calls to the field).

The LocationBarController and OmniboxViewIOS will continue to live in the
mediator for now.

                                WebOmniboxEditController* controller,
                                ios::ChromeBrowserState* browser_state,
                                id<PreloadProvider> preloader,
                                id<OmniboxPopupPositioner> positioner)
     : OmniboxView(
           controller,
           base::MakeUnique<ChromeOmniboxClientIOS>(controller, browser_state)),
       browser_state_(browser_state),
       field_(field),
       controller_(controller),
       preloader_(preloader),
       ignore_popup_updates_(false),
       attributing_display_string_(nil) {
+  DCHECK(field_);
   popup_view_.reset(new OmniboxPopupViewIOS(this, model(), positioner));
   field_delegate_.reset(
       [[AutocompleteTextFieldDelegate alloc] initWithEditView:this]);
   [field_ setDelegate:field_delegate_];
   [field_ addTarget:field_delegate_
                 action:@selector(textFieldDidChange:)
       forControlEvents:UIControlEventEditingChanged];
 }
 
 OmniboxViewIOS::~OmniboxViewIOS() {
@@ skipping 680 matching lines @@
 // is being left out for now because it was not present before the OmniboxView
 // rewrite.
 #if 0
   // When editing is in progress, the url text is not colored, so there is
   // nothing to emphasize.  (Calling SetText() in that situation would also be
   // harmful, as it would reset the carat position to the end of the text.)
   if (!IsEditingOrEmpty())
     SetText(GetText());
 #endif
 }