wasm: implement move for QWasmEventHandler

Implement move by copying the emscripten::val member
variables, and clearing the moved-from ones. This ensures
that the moved-from val is in a known state ("undefined").

Also move the non-default constructor declaration up to
the top of the class.

Change-Id: If9574cc91a53d4029d49b29b89819d98319acaa3
Reviewed-by: Even Oscar Andersen <even.oscar.andersen@qt.io>
Reviewed-by: Morten Johan Sørvig <morten.sorvig@qt.io>

src/corelib/platform/wasm/qwasmsuspendresumecontrol.cpp

@@ -180,12 +180,37 @@ QWasmEventHandler::QWasmEventHandler(emscripten::val element, const std::string
 
 QWasmEventHandler::~QWasmEventHandler()
 {
+    // Do nothing if this instance is default-constructed, or was moved from.
+    if (m_element.isUndefined())
+        return;
+
     QWasmSuspendResumeControl *suspendResume = QWasmSuspendResumeControl::get();
     Q_ASSERT(suspendResume);
     m_element.call<void>("removeEventListener", m_name, suspendResume->jsEventHandlerAt(m_eventHandlerIndex));
     suspendResume->removeEventHandler(m_eventHandlerIndex);
 }
 
+QWasmEventHandler::QWasmEventHandler(QWasmEventHandler&& other) noexcept
+:m_element(std::move(other.m_element))
+,m_name(std::move(other.m_name))
+,m_eventHandlerIndex(other.m_eventHandlerIndex)
+{
+    other.m_element = emscripten::val();
+    other.m_name = emscripten::val();
+    other.m_eventHandlerIndex = 0;
+}
+
+QWasmEventHandler& QWasmEventHandler::operator=(QWasmEventHandler&& other) noexcept
+{
+    m_element = std::move(other.m_element);
+    other.m_element = emscripten::val();
+    m_name = std::move(other.m_name);
+    other.m_name = emscripten::val();
+    m_eventHandlerIndex = other.m_eventHandlerIndex;
+    other.m_eventHandlerIndex = 0;
+    return *this;
+}
+
 //
 // The QWasmTimer class creates a native single-shot timer. The event handler is provided in the
 // constructor and can be reused: each call setTimeout() sets a new timeout, though with the

src/corelib/platform/wasm/qwasmsuspendresumecontrol_p.h

@@ -51,12 +51,13 @@ class Q_CORE_EXPORT QWasmEventHandler
 {
 public:
     QWasmEventHandler() = default;
+    QWasmEventHandler(emscripten::val element, const std::string &name,
+                      std::function<void(emscripten::val)> fn);
     ~QWasmEventHandler();
     QWasmEventHandler(QWasmEventHandler const&) = delete;
     QWasmEventHandler& operator=(QWasmEventHandler const&) = delete;
-    QWasmEventHandler(emscripten::val element, const std::string &name,
+    QWasmEventHandler(QWasmEventHandler&& other) noexcept;
-                      std::function<void(emscripten::val)> fn);
+    QWasmEventHandler& operator=(QWasmEventHandler&& other) noexcept;
-
 private:
     emscripten::val m_element;
     emscripten::val m_name;