bookmarks: Forward declare some classes in header files when possible.

chrome/browser/bookmarks/recently_used_folders_combo_model_unittest.cc

 // 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 "chrome/browser/bookmarks/recently_used_folders_combo_model.h"
 
 #include "base/memory/scoped_ptr.h"
 #include "base/utf_string_conversions.h"
+#include "chrome/browser/bookmarks/bookmark_model.h"
 #include "chrome/browser/bookmarks/bookmark_model_factory.h"
 #include "chrome/test/base/testing_profile.h"
 #include "content/public/test/test_browser_thread.h"
 #include "testing/gtest/include/gtest/gtest.h"
 
 using content::BrowserThread;
 
 class RecentlyUsedFoldersComboModelTest : public testing::Test {
  public:
   RecentlyUsedFoldersComboModelTest();
@@ skipping 36 matching lines @@
       bookmark_model->bookmark_bar_node(), 0, ASCIIToUTF16("a"),
       GURL("http://a"));
   RecentlyUsedFoldersComboModel model(bookmark_model, new_node);
   std::set<const BookmarkNode*> nodes;
   for (int i = 0; i < model.GetItemCount(); ++i) {
     const BookmarkNode* node = model.GetNodeAt(i);
     EXPECT_EQ(0u, nodes.count(node));
     nodes.insert(node);
   }
 }