Add support for loading extensions (issue #1947)

- Add CefRequestContext::LoadExtension, CefExtension, CefExtensionHandler and
  related methods/interfaces.
- Add chrome://extensions-support that lists supported Chrome APIs.
- Add CefBrowserHost::SetAutoResizeEnabled and CefDisplayHandler::OnAutoResize
  to support browser resize based on preferred web contents size.
- views: Add support for custom CefMenuButton popups.
- cefclient: Run with `--load-extension=set_page_color` command-line flag for
  an extension loading example. Add `--use-views` on Windows and Linux for an
  even better example.

tests/shared/browser/file_util.h

@@ -0,0 +1,45 @@
+// Copyright 2016 The Chromium Embedded Framework Authors. Portions copyright
+// 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.
+
+#ifndef CEF_TESTS_SHARED_BROWSER_FILE_UTIL_H_
+#define CEF_TESTS_SHARED_BROWSER_FILE_UTIL_H_
+#pragma once
+
+#include <limits>
+#include <string>
+
+namespace client {
+namespace file_util {
+
+// Platform-specific path separator.
+extern const char kPathSep;
+
+// Reads the file at |path| into |contents| and returns true on success and
+// false on error.  In case of I/O error, |contents| holds the data that could
+// be read from the file before the error occurred.  When the file size exceeds
+// max_size|, the function returns false with |contents| holding the file
+// truncated to |max_size|. |contents| may be NULL, in which case this function
+// is useful for its side effect of priming the disk cache (could be used for
+// unit tests). Calling this function on the browser process UI or IO threads is
+// not allowed.
+bool ReadFileToString(const std::string& path,
+                      std::string* contents,
+                      size_t max_size = std::numeric_limits<size_t>::max());
+
+// Writes the given buffer into the file, overwriting any data that was
+// previously there. Returns the number of bytes written, or -1 on error.
+// Calling this function on the browser process UI or IO threads is not allowed.
+int WriteFile(const std::string& path, const char* data, int size);
+
+// Combines |path1| and |path2| with the correct platform-specific path
+// separator.
+std::string JoinPath(const std::string& path1, const std::string& path2);
+
+// Extracts the file extension from |path|.
+std::string GetFileExtension(const std::string& path);
+
+}  // namespace file_util
+}  // namespace client
+
+#endif  // CEF_TESTS_SHARED_BROWSER_FILE_UTIL_H_