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/download_unittest.cc

@@ -5,9 +5,9 @@
 #include "include/cef_scheme.h"
 #include "include/wrapper/cef_closure_task.h"
 #include "include/wrapper/cef_scoped_temp_dir.h"
-#include "tests/ceftests/file_util.h"
 #include "tests/ceftests/test_handler.h"
 #include "tests/gtest/include/gtest/gtest.h"
+#include "tests/shared/browser/file_util.h"
 
 namespace {
 
@@ -155,7 +155,8 @@ class DownloadTestHandler : public TestHandler {
 
     // Create a new temporary directory.
     EXPECT_TRUE(temp_dir_.CreateUniqueTempDir());
-    test_path_ = file_util::JoinPath(temp_dir_.GetPath(), kTestFileName);
+    test_path_ =
+        client::file_util::JoinPath(temp_dir_.GetPath(), kTestFileName);
 
     if (test_mode_ == NAVIGATED) {
       // Add the resource that we'll navigate to.
@@ -318,7 +319,7 @@ class DownloadTestHandler : public TestHandler {
     if (test_mode_ != PENDING) {
       // Verify the file contents.
       std::string contents;
-      EXPECT_TRUE(file_util::ReadFileToString(test_path_, &contents));
+      EXPECT_TRUE(client::file_util::ReadFileToString(test_path_, &contents));
       EXPECT_STREQ(kTestContent, contents.c_str());
     }