Scroll by 3 pixels if sent from touchpad

ui/base/x/events_x.cc

 // Copyright (c) 2011 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 "ui/base/events.h"
 
 #include <X11/Xlib.h>
 #include <X11/extensions/XInput2.h>
 #include <string.h>
 
 #include "base/logging.h"
 #include "ui/base/keycodes/keyboard_code_conversion_x.h"
 #include "ui/base/touch/touch_factory.h"
 #include "ui/gfx/point.h"
 
 #if !defined(TOOLKIT_USES_GTK)
 #include "base/message_pump_x.h"
 #endif
 
 namespace {
 
 // Scroll amount for each wheelscroll event. 53 is also the value used for GTK+.
 static const int kWheelScrollAmount = 53;
 
 static const int kMinWheelButton = 4;
 #if defined(OS_CHROMEOS)
+// TODO(davemoore) For now use the button to decide how much to scroll by.
+// When we go to XI2 scroll events this won't be necessary. If this doesn't
+// happen for some reason we can better detect which devices are touchpads.
+static const int kTouchpadScrollAmount = 3;
 // Chrome OS also uses buttons 8 and 9 for scrolling.
 static const int kMaxWheelButton = 9;
 #else
 static const int kMaxWheelButton = 7;
 #endif
 
 int GetEventFlagsFromXState(unsigned int state) {
   int flags = 0;
   if (state & ControlMask)
     flags |= ui::EF_CONTROL_DOWN;
@@ skipping 268 matching lines @@
   if (native_event->type == GenericEvent) {
     XIDeviceEvent* xiev =
         static_cast<XIDeviceEvent*>(native_event->xcookie.data);
     button = xiev->detail;
   } else {
     button = native_event->xbutton.button;
   }
   switch (button) {
     case 4:
 #if defined(OS_CHROMEOS)
+      return kTouchpadScrollAmount;
     case 8:
 #endif
       return kWheelScrollAmount;
 
     case 5:
 #if defined(OS_CHROMEOS)
+      return -kTouchpadScrollAmount;
     case 9:
 #endif
       return -kWheelScrollAmount;
 
     default:
       // TODO(derat): Do something for horizontal scrolls (buttons 6 and 7)?
       return 0;
   }
 }
 
@@ skipping 67 matching lines @@
   // Make sure we use atom from current xdisplay, which may
   // change during the test.
   noop->xclient.message_type = XInternAtom(
       base::MessagePumpX::GetDefaultXDisplay(),
       "noop", False);
 #endif
   return noop;
 }
 
 }  // namespace ui