Remove the % WHEEL_DELTA check in WebMouseWheelEventBuilder.

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"
 #include "ui/events/blink/blink_event_util.h"
 #include "ui/events/event_utils.h"
@@ skipping 270 matching lines @@
 
     if (message == WM_HSCROLL)
       horizontal_scroll = true;
   } else {
     // Non-synthesized event; we can just read data off the event.
     key_state = GET_KEYSTATE_WPARAM(wparam);
 
     result.globalX = static_cast<short>(LOWORD(lparam));
     result.globalY = static_cast<short>(HIWORD(lparam));
 
-    short wheel_delta_wparam = GET_WHEEL_DELTA_WPARAM(wparam);
-    // The current heuristic for setting hasPreciseScrollingDelta is whether or
-    // not wheel_delta is an exact multiple of WHEEL_DELTA. Note that high
-    // precision trackpads can occasionally generate deltas that are an exact
-    // multiple of WHEEL_DELTA.
-    if (wheel_delta_wparam % WHEEL_DELTA != 0)
-      result.hasPreciseScrollingDeltas = true;
-
-    wheel_delta = static_cast<float>(wheel_delta_wparam);
+    // Currently we leave hasPreciseScrollingDeltas false, even for trackpad
+    // scrolls that generate WM_MOUSEWHEEL, since we don't have a good way to
+    // distinguish these from real mouse wheels (crbug.com/545234).
+    wheel_delta = static_cast<float>(GET_WHEEL_DELTA_WPARAM(wparam));
 
     if (message == WM_MOUSEHWHEEL) {
       horizontal_scroll = true;
       wheel_delta = -wheel_delta;  // Windows is <- -/+ ->, WebKit <- +/- ->.
     }
   }
   if (key_state & MK_SHIFT)
     horizontal_scroll = true;
 
   // Set modifiers based on key state.
@@ skipping 57 matching lines @@
     result.wheelTicksX = wheel_delta;
   } else {
     result.deltaY = scroll_delta;
     result.wheelTicksY = wheel_delta;
   }
 
   return result;
 }
 
 }  // namespace content