Fix duplicated application menu items on Mac OS

Added code to check to see if the menu item already exists in the
application menu before adding it.

Change-Id: Ie0a5eab3c61d5a3413a834d2e57bab40660f6802
Task-number: QTBUG-27202
Reviewed-by: Shawn Rutledge <shawn.rutledge@digia.com>

src/plugins/platforms/cocoa/qcocoamenuitem.mm

@@ -195,7 +195,7 @@ NSMenuItem *QCocoaMenuItem::sync()
         QT_MANGLE_NAMESPACE(QCocoaMenuLoader) *loader = getMenuLoader();
         switch (m_role) {
         case ApplicationSpecificRole:
-            mergeItem = [loader appSpecificMenuItem];
+            mergeItem = [loader appSpecificMenuItem:reinterpret_cast<NSInteger>(this)];
             break;
         case AboutRole:
             mergeItem = [loader aboutMenuItem];

src/plugins/platforms/cocoa/qcocoamenuloader.h

@@ -79,7 +79,7 @@
 - (NSMenuItem *)aboutMenuItem;
 - (NSMenuItem *)aboutQtMenuItem;
 - (NSMenuItem *)hideMenuItem;
-- (NSMenuItem *)appSpecificMenuItem;
+- (NSMenuItem *)appSpecificMenuItem:(NSInteger)tag;
 - (IBAction)terminate:(id)sender;
 - (IBAction)orderFrontStandardAboutPanel:(id)sender;
 - (IBAction)hideOtherApplications:(id)sender;

src/plugins/platforms/cocoa/qcocoamenuloader.mm

@@ -246,11 +246,17 @@ QT_END_NAMESPACE
     return [[hideItem retain] autorelease];
 }
 
-- (NSMenuItem *)appSpecificMenuItem
+- (NSMenuItem *)appSpecificMenuItem:(NSInteger)tag
 {
+    NSMenuItem *item = [appMenu itemWithTag:tag];
+
+    // No reason to create the item if it already exists. See QTBUG-27202.
+    if (item)
+        return [[item retain] autorelease];
+
     // Create an App-Specific menu item, insert it into the menu and return
     // it as an autorelease item.
-    NSMenuItem *item = [[NSMenuItem alloc] init];
+    item = [[NSMenuItem alloc] init];
 
     NSInteger location;
     if (lastAppSpecificItem == nil) {