UICommon: Add AutoUpdate module + placeholder Qt implementation

The AutoUpdate module is a generic update checker mechanism which can be
used by UI backends to trigger an auto-update check as well as the
actual update process.

Currently only configurable through .ini and the Qt implementation is
completely placeholder-y -- blocking the main thread on a network
request on startup, etc.

Source/Core/DolphinQt2/Main.cpp

@@ -7,6 +7,7 @@
 #include <QApplication>
 #include <QMessageBox>
 #include <QObject>
+#include <QWidget>
 
 #include "Common/MsgHandler.h"
 #include "Core/Analytics.h"
@@ -20,6 +21,7 @@
 #include "DolphinQt2/Resources.h"
 #include "DolphinQt2/Settings.h"
 #include "DolphinQt2/Translation.h"
+#include "UICommon/AutoUpdate.h"
 #include "UICommon/CommandLineParse.h"
 #include "UICommon/UICommon.h"
 
@@ -50,6 +52,35 @@ static bool QtMsgAlertHandler(const char* caption, const char* text, bool yes_no
   });
 }
 
+// TODO: This should be replaced with something in a background thread, it performs a blocking
+// HTTP query. It also needs a proper UI, and many other things. But right now it needs to be
+// manually enabled through INI, so all these problems are ignored :)
+class QtAutoUpdateChecker : public AutoUpdateChecker
+{
+public:
+  explicit QtAutoUpdateChecker(QWidget* parent) : m_parent(parent) {}
+protected:
+  void OnUpdateAvailable(const NewVersionInformation& info) override
+  {
+    QMessageBox prompt(m_parent);
+
+    prompt.setIcon(QMessageBox::Question);
+    prompt.setStandardButtons(QMessageBox::Yes | QMessageBox::No);
+    prompt.setText(QString::fromUtf8("Update Dolphin to version %1?")
+                       .arg(QString::fromStdString(info.new_shortrev)));
+
+    const int answer = prompt.exec();
+    if (answer == QMessageBox::Yes)
+    {
+      TriggerUpdate(info);
+      m_parent->close();
+    }
+  }
+
+private:
+  QWidget* m_parent;
+};
+
 // N.B. On Windows, this should be called from WinMain. Link against qtmain and specify
 // /SubSystem:Windows
 int main(int argc, char* argv[])
@@ -152,6 +183,9 @@ int main(int argc, char* argv[])
     }
 #endif
 
+    QtAutoUpdateChecker updater(&win);
+    updater.CheckForUpdate();
+
     retval = app.exec();
   }