Add scroll method to XiViewProxy

Sources/XiEditor/XiViewProxy.swift

@@ -28,6 +28,12 @@ protocol XiViewProxy: class {
     func copy() -> String?
     func cut() -> String?
 
+    /// Notifies the back-end of the visible scroll region, defined as the first and last
+    /// (non-inclusive) formatted lines. The visible scroll region is used to compute movement
+    /// distance for page up and page down commands, and also controls the size of the fragment
+    /// sent in the update method.
+    func scroll(firstLine: Int, lastLine: Int)
+
     func toggleRecording(name: String)
     func playRecording(name: String)
     func clearRecording(name: String)
@@ -104,6 +110,10 @@ final class XiViewConnection: XiViewProxy {
         }
     }
 
+    func scroll(firstLine: Int, lastLine: Int) {
+        sendRpcAsync("scroll", params: [firstLine, lastLine])
+    }
+
     func toggleRecording(name: String) {
         sendRpcAsync("toggle_recording", params: ["recording_name": name])
     }

Tests/XiEditorTests/XiViewProxyTests.swift

@@ -77,6 +77,19 @@ class XiViewProxyTests: XCTestCase {
         XCTAssertEqual(result!, testCopyCharacters)
     }
 
+    func testScroll() {
+        let asyncCalledExpectation = expectation(description: "Async should be called")
+        let async: XiViewConnection.AsyncRpc = { method, params, _ in
+            XCTAssertEqual("scroll", method)
+            let scrollParams = params as! [Int]
+            XCTAssertEqual([23, 42], scrollParams)
+            asyncCalledExpectation.fulfill()
+        }
+        let connection: XiViewProxy = XiViewConnection(asyncRpc: async, syncRpc: unusedSync)
+        connection.scroll(firstLine: 23, lastLine: 42)
+        wait(for: [asyncCalledExpectation], timeout: 1)
+    }
+
     func testToggleRecording() {
         let asyncCalledExpectation = expectation(description: "Async should be called")
         let async: XiViewConnection.AsyncRpc = { method, params,_ in