chrome: Support Chrome and DevTools command execution (fixes #3282, fixes #3600)

Add new CefBrowserHost::[Can]ExecuteChromeCommand methods for executing
arbitrary Chrome commands.

Add support for existing CefBrowserHost::ShowDevTools, CloseDevTools and
HasDevTools methods.

DevTools windows now support the same Views callbacks as normal popup
windows with the new CefLifeSpanHandler::OnBeforeDevToolsPopup callback
as the DevTools-specific equivalent of OnBeforePopup.

Always create DevTools as an undocked window to support use of
ShowDevTools with default Chrome browser windows.

To test:

Run `ceftests --enable-chrome-runtime [--use-views]
     --gtest_filter=V8Test.OnUncaughtExceptionDevTools`

OR:

1. Run `cefclient --enable-chrome-runtime [--use-native]`
2. Select "Show DevTools", "Close DevTools" or "Inspect" from the
   right-click menu.
3. Notice that the DevTools window is Views-hosted (or native-hosted)
   and works as expected.

Add --use-default-popup to get a default styled popup in step 3.

libcef_dll/ctocpp/life_span_handler_ctocpp.h

@@ -9,7 +9,7 @@
 // implementations. See the translator.README.txt file in the tools directory
 // for more information.
 //
-// $hash=229117f1ecb1cc27b5ab5eebd79e64c30d73a855$
+// $hash=53f00e60e361c79c69a8f19474a234d5011454f5$
 //
 
 #ifndef CEF_LIBCEF_DLL_CTOCPP_LIFE_SPAN_HANDLER_CTOCPP_H_
@@ -49,6 +49,12 @@ class CefLifeSpanHandlerCToCpp
                      CefBrowserSettings& settings,
                      CefRefPtr<CefDictionaryValue>& extra_info,
                      bool* no_javascript_access) override;
+  void OnBeforeDevToolsPopup(CefRefPtr<CefBrowser> browser,
+                             CefWindowInfo& windowInfo,
+                             CefRefPtr<CefClient>& client,
+                             CefBrowserSettings& settings,
+                             CefRefPtr<CefDictionaryValue>& extra_info,
+                             bool* use_default_window) override;
   void OnAfterCreated(CefRefPtr<CefBrowser> browser) override;
   bool DoClose(CefRefPtr<CefBrowser> browser) override;
   void OnBeforeClose(CefRefPtr<CefBrowser> browser) override;