Make SkOSWindow return the sample count and stencil bit count for its GL context.

src/views/ios/SkOSWindow_iOS.mm

 #import <UIKit/UIKit.h>
 #include "SkCanvas.h"
 #include "SkGraphics.h"
 #import "SkEventNotifier.h"
 #include "SkOSMenu.h"
 #include "SkTime.h"
 #include "SkTypes.h"
 #import "SkUIView.h"
 #include "SkWindow.h"
 
@@ skipping 33 matching lines @@
 
 void SkOSWindow::onAddMenu(const SkOSMenu* menu) {
     [(SkUIView*)fHWND onAddMenu:menu];
 }
 
 void SkOSWindow::onUpdateMenu(SkOSMenu* menu) {
     [(SkUIView*)fHWND onUpdateMenu:menu];
 }
 
 bool SkOSWindow::attach(SkBackEndTypes /* attachType */,
-                        int /* msaaSampleCount */) {
+                        int /* msaaSampleCount */,
+                        AttachmentInfo* info) {
+    [(SkUIView*)fHWND getAttachmentInfo:info];
     bool success = true;
     return success;
 }
 
 void SkOSWindow::detach() {}
 
 void SkOSWindow::present() {
 }