Bug 1325234 (part 3) - Streamline nsIWidget::Show(). r=mstange.

This patch changes it from |NS_IMETHOD| to |virtual void|. The return value was
only checked in one low-value assertion and one other place where the check had
no useful effect (in nsCocoaWindow::HideWindowChrome()).

widget/PuppetWidget.cpp

@@ -190,7 +190,7 @@ PuppetWidget::Destroy()
   mTabChild = nullptr;
 }
 
-NS_IMETHODIMP
+void
 PuppetWidget::Show(bool aState)
 {
   NS_ASSERTION(mEnabled,
@@ -216,8 +216,6 @@ PuppetWidget::Show(bool aState)
     Resize(mBounds.width, mBounds.height, false);
     Invalidate(mBounds);
   }
-
-  return NS_OK;
 }
 
 void