Fix overflow/underflow in gfx geometry once and for all

chrome/browser/chromeos/accessibility/accessibility_highlight_manager.cc

 // Copyright (c) 2016 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 "ash/shell.h"
 #include "chrome/browser/chromeos/accessibility/accessibility_highlight_manager.h"
 #include "chrome/browser/chromeos/ui/accessibility_focus_ring_controller.h"
 #include "content/public/browser/focused_node_details.h"
 #include "content/public/browser/notification_service.h"
 #include "content/public/browser/notification_types.h"
 #include "ui/aura/window_tree_host.h"
 #include "ui/wm/core/cursor_manager.h"
 
 namespace chromeos {
 
 namespace {
 
+// TODO: don't hide carets and focus ring "offscreen" by using large numbers.
 const gfx::Rect& OffscreenRect() {
-  CR_DEFINE_STATIC_LOCAL(const gfx::Rect, r, (INT_MIN, INT_MIN, 0, 0));
+  CR_DEFINE_STATIC_LOCAL(const gfx::Rect, r,
+                         (INT_MAX - 1000, INT_MAX - 1000, 0, 0));

[enne (OOO), 2016/09/23 00:17:06]

Surprisingly, AccessibilityHighlightManagerTest.TestFocusRingDrawsOrangePixels
depends on the fact that the offscreen rect is a large *positive* number when
inset by 40 pixels.  This is an integer underflow and undefined behavior.

If I make it INT_MIN + 1000, the test also fails but with a different error
(wrong pixels).  Therefore, it appears that this test relies on very specific
offscreen point values.  So, I've made it use large positive numbers with enough
of an offset that it won't overflow when inset by margins.

I'm kind of surprised that there's not some more straight forward way to convey
the information that the focus ring or caret should be invisible instead of just
placing it very far away.

[dmazzoni, 2016/10/04 22:29:32]

Working on a cleaner fix for this here:

https://codereview.chromium.org/2388093004/

   return r;
 }
 
 const gfx::Point& OffscreenPoint() {
-  CR_DEFINE_STATIC_LOCAL(const gfx::Point, p, (INT_MIN, INT_MIN));
+  CR_DEFINE_STATIC_LOCAL(const gfx::Point, p, (INT_MAX - 1000, INT_MAX - 1000));
   return p;
 }
 
 ui::InputMethod* GetInputMethod(aura::Window* root_window) {
   if (root_window->GetHost())
     return root_window->GetHost()->GetInputMethod();
   return nullptr;
 }
 
 }  // namespace
@@ skipping 134 matching lines @@
   if (!cursor_)
     point = OffscreenPoint();
 
   if (!IsCursorVisible())
     point = OffscreenPoint();
 
   AccessibilityFocusRingController::GetInstance()->SetCursorRing(point);
 }
 
 }  // namespace chromeos