Fix for the continuing issues with pointer lock operations in HiDPI Chrome.

content/browser/renderer_host/render_widget_host_view_aura.cc

 // Copyright (c) 2012 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/render_widget_host_view_aura.h"
 
 #include "base/auto_reset.h"
 #include "base/basictypes.h"
 #include "base/bind.h"
 #include "base/callback_helpers.h"
@@ skipping 1906 matching lines @@
       window_->MoveCursorTo(center);
       return;
     }
 
     blink::WebMouseEvent mouse_event = MakeWebMouseEvent(*event);
 
     bool is_move_to_center_event = (event->type() == ui::ET_MOUSE_MOVED ||
         event->type() == ui::ET_MOUSE_DRAGGED) &&
         mouse_event.x == center.x() && mouse_event.y == center.y();
 
+    // For fractional scale factors, the conversion from pixels to dip and
+    // vice versa could result in off by 1 or 2 errors which hurts us because
+    // we want to avoid sending the artificial move to center event to the
+    // renderer. Sending the move to center to the renderer cause the cursor
+    // to bounce around the center of the screen leading to the lock operation
+    // not working correctly.
+    // Workaround is to treat a mouse move or drag event off by at most 2 px
+    // from the center as a move to center event.
+    if (synthetic_move_sent_ && (current_device_scale_factor_ != 1)) {

[cpu_(ooo_6.6-7.5), 2015/03/19 03:06:11]

but !=1 does not mean fractional scale ..

[ananta, 2015/03/19 19:49:17]

Yeah. I added a function called IsFractionalScaleFactor which returns true for a
fractional scale factor.

+      if (event->type() == ui::ET_MOUSE_MOVED ||
+          event->type() == ui::ET_MOUSE_DRAGGED) {
+        if ((abs(mouse_event.x - center.x()) <= 2) &&
+            (abs(mouse_event.y - center.y()) <= 2)) {
+          is_move_to_center_event = true;
+        }
+      }
+    }
+
     ModifyEventMovementAndCoords(&mouse_event);
 
     bool should_not_forward = is_move_to_center_event && synthetic_move_sent_;
     if (should_not_forward) {
       synthetic_move_sent_ = false;
     } else {
       // Check if the mouse has reached the border and needs to be centered.
       if (ShouldMoveToCenter()) {
         synthetic_move_sent_ = true;
         window_->MoveCursorTo(center);
@@ skipping 744 matching lines @@
 
 ////////////////////////////////////////////////////////////////////////////////
 // RenderWidgetHostViewBase, public:
 
 // static
 void RenderWidgetHostViewBase::GetDefaultScreenInfo(WebScreenInfo* results) {
   GetScreenInfoForWindow(results, NULL);
 }
 
 }  // namespace content