Fix scroll_delta computation on windows for vertical scroll by page

content/browser/renderer_host/input/web_input_event_builders_win.cc

 // Copyright 2013 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.
 
 #include "content/browser/renderer_host/input/web_input_event_builders_win.h"
 
 #include "base/logging.h"
 #include "content/browser/renderer_host/input/web_input_event_util.h"
 
 using WebKit::WebInputEvent;
@@ skipping 410 matching lines @@
   // page or go to different pages.  IE 8 is ~60 px/line, although the value
   // seems to vary slightly by page and zoom level.  Also, IE defaults to
   // smooth scrolling while Firefox doesn't, so it can get away with somewhat
   // larger scroll values without feeling as jerky.  Here we use 100 px per
   // three lines (the default scroll amount is three lines per wheel tick).
   // Even though we have smooth scrolling, we don't make this as large as IE
   // because subjectively IE feels like it scrolls farther than you want while
   // reading articles.
   static const float kScrollbarPixelsPerLine = 100.0f / 3.0f;
   wheel_delta /= WHEEL_DELTA;
-  float scroll_delta = wheel_delta * kScrollbarPixelsPerLine;
+  float scroll_delta = wheel_delta;
   if (horizontal_scroll) {
     unsigned long scroll_chars = kDefaultScrollCharsPerWheelDelta;
     SystemParametersInfo(SPI_GETWHEELSCROLLCHARS, 0, &scroll_chars, 0);
     // TODO(pkasting): Should probably have a different multiplier
     // scrollbarPixelsPerChar here.
-    scroll_delta *= static_cast<float>(scroll_chars);
+    scroll_delta *= static_cast<float>(scroll_chars) * kScrollbarPixelsPerLine;
   } else {
     unsigned long scroll_lines = kDefaultScrollLinesPerWheelDelta;
     SystemParametersInfo(SPI_GETWHEELSCROLLLINES, 0, &scroll_lines, 0);
     if (scroll_lines == WHEEL_PAGESCROLL)
       result.scrollByPage = true;
-    if (!result.scrollByPage)
-      scroll_delta *= static_cast<float>(scroll_lines);
+    if (!result.scrollByPage) {
+      scroll_delta *=
+          static_cast<float>(scroll_lines) * kScrollbarPixelsPerLine;
+    }
   }
 
   // Set scroll amount based on above calculations.  WebKit expects positive
   // deltaY to mean "scroll up" and positive deltaX to mean "scroll left".
   if (horizontal_scroll) {
     result.deltaX = scroll_delta;
     result.wheelTicksX = wheel_delta;
   } else {
     result.deltaY = scroll_delta;
     result.wheelTicksY = wheel_delta;
   }
 
   return result;
 }
 
 }  // namespace content