OOP PDF: Fix incorrect scrolling during fit-to-page

chrome/test/data/pdf/viewport_test.js

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 var tests = [
   function testDocumentNeedsScrollbars() {
     var viewport =
         new Viewport(new MockWindow(100, 100), new MockSizer(), function() {},
                      function() {}, function() {}, 10, 0);
     var scrollbars;
@@ skipping 291 matching lines @@
     viewport.fitToPage();
     chrome.test.assertEq(0.5, viewport.zoom);
     chrome.test.assertEq(0, viewport.position.x);
     chrome.test.assertEq(0, viewport.position.y);
     viewport.setZoom(1);
     mockWindow.scrollTo(0, 175);
     viewport.fitToPage();
     chrome.test.assertEq(0.25, viewport.zoom);
     chrome.test.assertEq(0, viewport.position.x);
     chrome.test.assertEq(50, viewport.position.y);
+
+    // Test that when the window size changes, fit-to-page occurs but does not
+    // scroll to the top of the page (it should stay at the scaled scroll
+    // position).
+    mockWindow.scrollTo(0, 0);
+    viewport.fitToPage();
+    chrome.test.assertEq(0.5, viewport.zoom);
+    mockWindow.scrollTo(0, 10);
+    mockWindow.setSize(50, 50);
+    chrome.test.assertEq(0.25, viewport.zoom);
+    chrome.test.assertEq(0, viewport.position.x);
+    chrome.test.assertEq(5, viewport.position.y);
+
     chrome.test.succeed();
   },
 
   function testGoToPage() {
     var mockWindow = new MockWindow(100, 100);
     var mockSizer = new MockSizer();
     var mockCallback = new MockViewportChangedCallback();
     var viewport = new Viewport(mockWindow, mockSizer, mockCallback.callback,
                                 function() {}, function() {}, 0, 0);
     var documentDimensions = new MockDocumentDimensions();
@@ skipping 91 matching lines @@
         chrome.test.assertEq(1, viewport.zoom);
     };
     viewport = new Viewport(mockWindow, mockSizer, function() {},
                             beforeZoom, afterZoom, 0, 0);
     viewport.setZoom(0.5);
     chrome.test.succeed();
   }
 ];
 
 chrome.test.runTests(tests);