Fix Ctrl-A then Ctrl-X infinite loop in quick_launch.

mash/quick_launch/quick_launch.cc

 // 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.
 
 #include "mash/quick_launch/quick_launch.h"
 
 #include "base/macros.h"
 #include "base/memory/ptr_util.h"
 #include "base/message_loop/message_loop.h"
 #include "base/strings/string16.h"
@@ skipping 78 matching lines @@
       UpdateEntries();
     }
     return false;
   }
   void ContentsChanged(views::Textfield* sender,
                        const base::string16& new_contents) override {
     // Don't keep making a suggestion if the user didn't like what we offered.
     if (suggestion_rejected_)
       return;
 
+    if (new_contents.empty())
+      return;
+
     // TODO(beng): it'd be nice if we persisted some history/scoring here.
     for (const auto& name : app_names_) {
       if (base::StartsWith(name, new_contents,
                            base::CompareCase::INSENSITIVE_ASCII)) {
         base::string16 suffix = name;
         base::ReplaceSubstringsAfterOffset(&suffix, 0, new_contents,
                                            base::string16());
         gfx::Range range(static_cast<uint32_t>(new_contents.size()),
                          static_cast<uint32_t>(name.size()));
         prompt_->SetText(name);
@@ skipping 91 matching lines @@
   windows_.push_back(window);
 }
 
 void QuickLaunch::Create(const service_manager::Identity& remote_identity,
                          mojom::LaunchableRequest request) {
   bindings_.AddBinding(this, std::move(request));
 }
 
 }  // namespace quick_launch
 }  // namespace mash