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/browser/chrome/views/chrome_browser_frame.cc

@@ -4,6 +4,8 @@
 
 #include "libcef/browser/chrome/views/chrome_browser_frame.h"
 
+#include "libcef/browser/chrome/chrome_browser_host_impl.h"
+
 #include "chrome/browser/themes/theme_service.h"
 #include "chrome/browser/ui/browser.h"
 #include "chrome/browser/ui/browser_commands.h"
@@ -57,3 +59,24 @@ ChromeBrowserFrame::CreateNonClientFrameView() {
   // Bypass the BrowserFrame implementation.
   return views::Widget::CreateNonClientFrameView();
 }
+
+void ChromeBrowserFrame::Activate() {
+  if (browser_view_ && browser_view_->browser() &&
+      browser_view_->browser()->is_type_devtools()) {
+    if (auto browser_host = ChromeBrowserHostImpl::GetBrowserForBrowser(
+            browser_view_->browser())) {
+      if (browser_host->platform_delegate()->HasExternalParent()) {
+        // Handle activation of DevTools with external parent via the platform
+        // delegate. On Windows the default platform implementation
+        // (HWNDMessageHandler::Activate) will call SetForegroundWindow but that
+        // doesn't seem to work for DevTools windows when activated via the
+        // right-click context menu.
+        browser_host->SetFocus(true);
+        return;
+      }
+    }
+  }
+
+  // Proceed with default handling.
+  BrowserFrame::Activate();
+}