Fix scrollbar overflow with ScaleToEnclosingRectSafe

ui/gfx/geometry/rect.h

 // 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.
 
 // Defines a simple integer rectangle class.  The containment semantics
 // are array-like; that is, the coordinate (x, y) is considered to be
 // contained by the rectangle, but the coordinate (x + width, y) is not.
 // The class will happily let you create malformed rectangles (that is,
 // rectangles with negative width and/or height), but there will be assertions
 // in the operations (such as Contains()) to complain in this case.
@@ skipping 266 matching lines @@
       x : static_cast<int>(std::ceil(rect.right() * x_scale));
   int b = rect.height() == 0 ?
       y : static_cast<int>(std::ceil(rect.bottom() * y_scale));
   return Rect(x, y, r - x, b - y);
 }
 
 inline Rect ScaleToEnclosingRect(const Rect& rect, float scale) {
   return ScaleToEnclosingRect(rect, scale, scale);
 }
 
+// ScaleToEnclosingRect but clamping instead of asserting if the resulting rect
+// would overflow.
+inline Rect ScaleToEnclosingRectSafe(const Rect& rect,
+                                     float x_scale,
+                                     float y_scale) {
+  if (x_scale == 1.f && y_scale == 1.f)
+    return rect;
+  int x = base::saturated_cast<int>(std::floor(rect.x() * x_scale));
+  int y = base::saturated_cast<int>(std::floor(rect.y() * y_scale));
+  int w = base::saturated_cast<int>(std::ceil(rect.width() * x_scale));
+  int h = base::saturated_cast<int>(std::ceil(rect.height() * y_scale));
+  return Rect(x, y, w, h);
+}
+
+inline Rect ScaleToEnclosingRectSafe(const Rect& rect, float scale) {
+  return ScaleToEnclosingRectSafe(rect, scale, scale);
+}
+
 inline Rect ScaleToEnclosedRect(const Rect& rect,

[danakj, 2016/10/04 21:32:51]

Leave a comment here to use ScaleToEnclosingRectSafe() if the inputs are not
known to result in valid integer outputs?

                                 float x_scale,
                                 float y_scale) {
   if (x_scale == 1.f && y_scale == 1.f)
     return rect;
   DCHECK(base::IsValueInRangeForNumericType<int>(
       std::ceil(rect.x() * x_scale)));
   DCHECK(base::IsValueInRangeForNumericType<int>(
       std::ceil(rect.y() * y_scale)));
   DCHECK(base::IsValueInRangeForNumericType<int>(
       std::floor(rect.right() * x_scale)));
@@ skipping 13 matching lines @@
 }
 
 // This is declared here for use in gtest-based unit tests but is defined in
 // the //ui/gfx:test_support target. Depend on that to use this in your unit
 // test. This should not be used in production code - call ToString() instead.
 void PrintTo(const Rect& rect, ::std::ostream* os);
 
 }  // namespace gfx
 
 #endif  // UI_GFX_GEOMETRY_RECT_H_