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/ceftests/test_suite.cc

@@ -4,6 +4,7 @@
 
 #include "tests/ceftests/test_suite.h"
 
+#include "include/cef_file_util.h"
 #include "tests/gtest/include/gtest/gtest.h"
 #include "tests/shared/common/client_switches.h"
 
@@ -162,6 +163,19 @@ bool CefTestSuite::GetCachePath(std::string& path) const {
   return false;
 }
 
+void CefTestSuite::RegisterTempDirectory(const CefString& directory) {
+  base::AutoLock lock_scope(temp_directories_lock_);
+  temp_directories_.push_back(directory);
+}
+
+void CefTestSuite::DeleteTempDirectories() {
+  base::AutoLock lock_scope(temp_directories_lock_);
+  for (size_t i = 0U; i < temp_directories_.size(); ++i) {
+    CefDeleteFile(temp_directories_[i], true);
+  }
+  temp_directories_.clear();
+}
+
 void CefTestSuite::PreInitialize() {
 #if defined(OS_WIN)
   testing::GTEST_FLAG(catch_exceptions) = false;