Mac: Make shift-space scroll up even when the detail view doesn't have focus

Issue #969.

Mac/MainWindow/Detail/DetailViewController.swift

@@ -66,9 +66,17 @@ final class DetailViewController: NSViewController, WKUIDelegate {
 		currentWebViewController.canScrollDown(callback)
 	}
 
+	func canScrollUp(_ callback: @escaping (Bool) -> Void) {
+		currentWebViewController.canScrollUp(callback)
+	}
+
 	override func scrollPageDown(_ sender: Any?) {
 		currentWebViewController.scrollPageDown(sender)
 	}
+
+	override func scrollPageUp(_ sender: Any?) {
+		currentWebViewController.scrollPageUp(sender)
+	}
 	
 	// MARK: - Navigation
 	

Mac/MainWindow/Detail/DetailWebViewController.swift

@@ -167,9 +167,19 @@ final class DetailWebViewController: NSViewController, WKUIDelegate {
 		}
 	}
 
+	func canScrollUp(_ completion: @escaping (Bool) -> Void) {
+		fetchScrollInfo { (scrollInfo) in
+			completion(scrollInfo?.canScrollUp ?? false)
+		}
+	}
+
 	override func scrollPageDown(_ sender: Any?) {
 		webView.scrollPageDown(sender)
 	}
+
+	override func scrollPageUp(_ sender: Any?) {
+		webView.scrollPageUp(sender)
+	}
 }
 
 // MARK: - WKScriptMessageHandler

Mac/MainWindow/MainWindowController.swift

@@ -264,6 +264,19 @@ class MainWindowController : NSWindowController, NSUserInterfaceValidations {
 		}
 	}
 
+	@IBAction func scrollUp(_ sender: Any?) {
+		guard let detailViewController = detailViewController else {
+			return
+		}
+		detailViewController.canScrollUp { (canScroll) in
+			if (canScroll) {
+				NSCursor.setHiddenUntilMouseMoves(true)
+				detailViewController.scrollPageUp(sender)
+			}
+		}
+
+	}
+
 	@IBAction func openArticleInBrowser(_ sender: Any?) {
 		if let link = currentLink {
 			Browser.open(link, invertPreference: NSApp.currentEvent?.modifierFlags.contains(.shift) ?? false)

Shared/Resources/GlobalKeyboardShortcuts.plist

@@ -10,6 +10,16 @@
 		<key>action</key>
 		<string>scrollOrGoToNextUnread:</string>
 	</dict>
+	<dict>
+		<key>title</key>
+		<string>Scroll or Go to Next Unread</string>
+		<key>key</key>
+		<string>[space]</string>
+		<key>shiftModifier</key>
+		<true/>
+		<key>action</key>
+		<string>scrollUp:</string>
+	</dict>
 	<dict>
 		<key>title</key>
 		<string>Go to Previous Unread</string>