cros: Fix crash when opening keyboard shortcut overlay from settings

Crash was introduced in commit 8f1e606d

More than one part of chrome calls mojo methods in NewWindowController,
so there can be more than one binding. I've audited the other changes
in the above CL and they should be OK, so keeping this change small
for easier backport.

Bug: 794581
Test: ash_unittests, chrome unit_tests and browser_tests, manually open keyboard shortcut overlay from webui settings > keyboard section
Change-Id: I6b274ecd7b8e6c0c366c36a398e9094b4c361dd9
Reviewed-on: https://chromium-review.googlesource.com/826026Reviewed-by: Michael Wasserman <msw@chromium.org>
Commit-Queue: James Cook <jamescook@chromium.org>
Cr-Commit-Position: refs/heads/master@{#523969}

ash/new_window_controller.cc

@@ -8,13 +8,13 @@
 
 namespace ash {
 
-NewWindowController::NewWindowController() : binding_(this) {}
+NewWindowController::NewWindowController() = default;
 
 NewWindowController::~NewWindowController() = default;
 
 void NewWindowController::BindRequest(
     mojom::NewWindowControllerRequest request) {
-  binding_.Bind(std::move(request));
+  bindings_.AddBinding(this, std::move(request));
 }
 
 void NewWindowController::SetClient(

ash/new_window_controller.h

@@ -9,7 +9,7 @@
 #include "ash/public/interfaces/new_window.mojom.h"
 #include "base/macros.h"
 #include "mojo/public/cpp/bindings/associated_binding.h"
-#include "mojo/public/cpp/bindings/binding.h"
+#include "mojo/public/cpp/bindings/binding_set.h"
 
 namespace ash {
 
@@ -38,7 +38,9 @@ class ASH_EXPORT NewWindowController : public mojom::NewWindowController {
   void OpenFeedbackPage();
 
  private:
-  mojo::Binding<mojom::NewWindowController> binding_;
+  // More than one part of chrome may connect to call the mojo methods, so use
+  // BindingSet instead of Binding. http://crbug.com/794581
+  mojo::BindingSet<mojom::NewWindowController> bindings_;
 
   mojom::NewWindowClientAssociatedPtr client_;