Bring mac code into conformance with -Wobjc-missing-property-synthesis

atom/browser/native_browser_view_mac.mm

@@ -25,6 +25,8 @@ const NSAutoresizingMaskOptions kDefaultAutoResizingMask =
 
 @implementation DragRegionView
 
+@synthesize initialLocation;
+
 - (BOOL)mouseDownCanMoveWindow
 {
   return NO;

atom/browser/native_window_mac.mm

@@ -425,6 +425,9 @@ bool ScopedDisableResize::disable_resize_ = false;
 
 @implementation AtomPreviewItem
 
+@synthesize previewItemURL;
+@synthesize previewItemTitle;
+
 - (id)initWithURL:(NSURL*)url title:(NSString*)title {
   self = [super init];
   if (self) {
@@ -480,6 +483,13 @@ enum {
 
 @implementation AtomNSWindow
 
+@synthesize acceptsFirstMouse;
+@synthesize disableAutoHideCursor;
+@synthesize disableKeyOrMainWindow;
+@synthesize windowButtonsOffset;
+@synthesize quickLookItem;
+@synthesize vibrantView;
+
 - (void)setShell:(atom::NativeWindowMac*)shell {
   shell_ = shell;
 }

atom/browser/ui/file_dialog_mac.mm

@@ -27,6 +27,9 @@
 
 @implementation PopUpButtonHandler
 
+@synthesize savePanel;
+@synthesize fileTypesList;
+
 - (instancetype)initWithPanel:(NSSavePanel*)panel
                  andTypesList:(NSArray*)typesList {
   self = [super init];