Add plugin placeholder and policy support (issue #1708)

- Default plugin loading policy can be specified using the new
  `--plugin-policy=[allow|block|detect]` command-line flag.
- Move CefRequestHandler::OnBeforePluginLoad to
  CefRequestContextHandler and add a new policy argument that
  supports different actions (allow, block, detect, disable) on a
  per-plugin-instance basis.
- Add CefContextMenuHandler::RunContextMenu for providing a custom
  context menu implementation.
- Add CefResourceBundleHandler::GetDataResourceForScale for
  returning scaled resources (issue #1272).
- Add CefResourceBundle for retrieving resources from the resource
  bundle (*.pak) files loaded by CEF during startup or via the
  CefResourceBundleHandler.
- Linux: Fix Debug build IO access warning with CefGetMimeType.
- cef_unittests: Move the refcounting implementation from TestHandler
  to subclasses in order to support interface inheritance from
  subclasses.

libcef/common/resource_bundle_impl.cc

@@ -0,0 +1,47 @@
+// Copyright (c) 2015 The Chromium Embedded Framework 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 "libcef/common/resource_bundle_impl.h"
+
+#include "ui/base/resource/resource_bundle.h"
+
+CefResourceBundleImpl::CefResourceBundleImpl() {
+}
+
+CefString CefResourceBundleImpl::GetLocalizedString(int string_id) {
+  if (!ui::ResourceBundle::HasSharedInstance())
+    return CefString();
+
+  return ui::ResourceBundle::GetSharedInstance().GetLocalizedString(string_id);
+}
+
+bool CefResourceBundleImpl::GetDataResource(int resource_id,
+                                            void*& data,
+                                            size_t& data_size) {
+  return GetDataResourceForScale(resource_id, SCALE_FACTOR_NONE, data,
+                                 data_size);
+}
+
+bool CefResourceBundleImpl::GetDataResourceForScale(int resource_id,
+                                                    ScaleFactor scale_factor,
+                                                    void*& data,
+                                                    size_t& data_size) {
+  if (!ui::ResourceBundle::HasSharedInstance())
+    return false;
+
+  const base::StringPiece& result =
+      ui::ResourceBundle::GetSharedInstance().GetRawDataResourceForScale(
+          resource_id, static_cast<ui::ScaleFactor>(scale_factor));
+  if (result.empty())
+    return false;
+
+  data = const_cast<char*>(result.data());
+  data_size = result.size();
+  return true;
+}
+
+// static
+CefRefPtr<CefResourceBundle> CefResourceBundle::GetGlobal() {
+  return new CefResourceBundleImpl();
+}