Fix an issue with not clearing |selected_text_| when text selection range is empty (Mac)

content/browser/renderer_host/render_widget_host_view_mac.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 "content/browser/renderer_host/render_widget_host_view_mac.h"
 
 #import <Carbon/Carbon.h>
 #import <objc/runtime.h>
 #include <OpenGL/gl.h>
 #include <QuartzCore/QuartzCore.h>
@@ skipping 993 matching lines @@
   DCHECK_EQ(GetTextInputManager(), text_input_manager);
 
   RenderWidgetHostViewBase* focused_view = GetFocusedViewForTextSelection();
   if (!focused_view)
     return;
 
   const TextInputManager::TextSelection* selection =
       GetTextInputManager()->GetTextSelection(focused_view);
 
   base::string16 text;
-  if (selection->GetSelectedText(&text))
-    selected_text_ = base::UTF16ToUTF8(text);
+  if (!selection->GetSelectedText(&text))
+    return;
+  selected_text_ = base::UTF16ToUTF8(text);
 
   [cocoa_view_ setSelectedRange:selection->range.ToNSRange()];
   // Updates markedRange when there is no marked text so that retrieving
   // markedRange immediately after calling setMarkdText: returns the current
   // caret position.
   if (![cocoa_view_ hasMarkedText]) {
     [cocoa_view_ setMarkedRange:selection->range.ToNSRange()];
   }
 
   // TODO(ekaramad): The following values are tracked by TextInputManager and
@@ skipping 2422 matching lines @@
 
 // "-webkit-app-region: drag | no-drag" is implemented on Mac by excluding
 // regions that are not draggable. (See ControlRegionView in
 // native_app_window_cocoa.mm). This requires the render host view to be
 // draggable by default.
 - (BOOL)mouseDownCanMoveWindow {
   return YES;
 }
 
 @end