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/browser_host_ctocpp.h

@@ -9,7 +9,7 @@
 // implementations. See the translator.README.txt file in the tools directory
 // for more information.
 //
-// $hash=5c1df6572bffebd983970394be27397837db0b25$
+// $hash=e07873b7e67c06fb54dafa370eca83d2c698ffb9$
 //
 
 #ifndef CEF_LIBCEF_DLL_CTOCPP_BROWSER_HOST_CTOCPP_H_
@@ -136,6 +136,9 @@ class CefBrowserHostCToCpp : public CefCToCppRefCounted<CefBrowserHostCToCpp,
   bool IsAudioMuted() override;
   bool IsFullscreen() override;
   void ExitFullscreen(bool will_cause_resize) override;
+  bool CanExecuteChromeCommand(int command_id) override;
+  void ExecuteChromeCommand(int command_id,
+                            cef_window_open_disposition_t disposition) override;
 };
 
 #endif  // CEF_LIBCEF_DLL_CTOCPP_BROWSER_HOST_CTOCPP_H_