Return version information for wxWebViewChromium

This can be useful for diagnostic purposes and looks better than "0.0"
in the webview sample.

Notice that currently we return the compile-time version and not the
run-time version that could be retrieved using cef_version_info()
because this is simpler and we shouldn't be ever using a different
version from the one we were compiled with anyhow.

samples/webview/webview.cpp

@@ -483,7 +483,7 @@ WebFrame::WebFrame(const wxString& url, bool isMain, wxWebViewWindowFeatures* wi
     {
         // Log backend information
         wxLogMessage("Backend: %s Version: %s", m_browser->GetClassInfo()->GetClassName(),
-            wxWebView::GetBackendVersionInfo().ToString());
+            wxWebView::GetBackendVersionInfo(backend).ToString());
 
         // Chromium backend can't be used immediately after creation, so wait
         // until the browser is created before calling GetUserAgent().

src/common/webview_chromium.cpp

@@ -1475,6 +1475,18 @@ public:
 
         return true;
     }
+
+    virtual wxVersionInfo GetVersionInfo() override
+    {
+        return {
+            "CEF",
+            CEF_VERSION_MAJOR,
+            CEF_VERSION_MINOR,
+            CEF_VERSION_PATCH,
+            CEF_COMMIT_NUMBER,
+            CEF_VERSION
+        };
+    }
 };
 
 class wxWebViewChromiumModule : public wxModule