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.

patch/patch.cfg

@@ -117,6 +117,10 @@ patches = [
     # Windows: Fix incorrect DIPToScreenRect usage in DesktopWindowTreeHostWin
     # when |has_external_parent_| is true.
     # https://github.com/chromiumembedded/cef/issues/3359
+    #
+    # chrome: Allow override of Widget::Activate() to support activation of
+    # DevTools windows with external parent.
+    # https://github.com/chromiumembedded/cef/issues/3282
     'name': 'views_widget',
   },
   {