cefclient: win: Add code signing verification (see #3935)

Move code signing verification code to libcef_dll_wrapper
and add example checks in cefclient.

Load libcef.dll with code signing checks.

Add a CefScopedLibraryLoader variant for Windows.

cef_paths2.gypi

@@ -80,6 +80,11 @@
     'includes_wrapper_mac': [
       'include/wrapper/cef_library_loader.h',
     ],
+    'includes_wrapper_win': [
+      'include/wrapper/cef_certificate_util_win.h',
+      'include/wrapper/cef_library_loader.h',
+      'include/wrapper/cef_util_win.h',
+    ],
     'includes_win': [
       'include/cef_sandbox_win.h',
       'include/internal/cef_win.h',
@@ -166,10 +171,15 @@
       'libcef_dll/wrapper/libcef_dll_wrapper2.cc',
     ],
     'libcef_dll_wrapper_sources_mac': [
-      'libcef_dll/wrapper/cef_library_loader_mac.mm',
+      'libcef_dll/wrapper/cef_scoped_library_loader_mac.mm',
       'libcef_dll/wrapper/cef_scoped_sandbox_context_mac.mm',
       'libcef_dll/wrapper/libcef_dll_dylib.cc',
     ],
+    'libcef_dll_wrapper_sources_win': [
+      'libcef_dll/wrapper/cef_certificate_util_win.cc',
+      'libcef_dll/wrapper/cef_scoped_library_loader_win.cc',
+      'libcef_dll/wrapper/cef_util_win.cc',
+    ],
     'shared_sources_browser': [
       'tests/shared/browser/client_app_browser.cc',
       'tests/shared/browser/client_app_browser.h',