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 236 matching lines @@
 GFX_EXPORT Rect SubtractRects(const Rect& a, const Rect& b);
 
 // Constructs a rectangle with |p1| and |p2| as opposite corners.
 //
 // This could also be thought of as "the smallest rect that contains both
 // points", except that we consider points on the right/bottom edges of the
 // rect to be outside the rect.  So technically one or both points will not be
 // contained within the rect, because they will appear on one of these edges.
 GFX_EXPORT Rect BoundingRect(const Point& p1, const Point& p2);
 
+// Scales the rect and returns the enclosing rect.  Use this only the inputs are
+// known to not overflow.  Use ScaleToEnclosingRectSafe if the inputs are
+// unknown and need to use saturated math.
 inline Rect ScaleToEnclosingRect(const Rect& rect,
                                  float x_scale,
                                  float y_scale) {
   if (x_scale == 1.f && y_scale == 1.f)
     return rect;
   // These next functions cast instead of using e.g. ToFlooredInt() because we
   // haven't checked to ensure that the clamping behavior of the helper
   // functions doesn't degrade performance, and callers shouldn't be passing
   // values that cause overflow anyway.
   DCHECK(base::IsValueInRangeForNumericType<int>(
@@ skipping 10 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,
                                 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>(
@@ skipping 14 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_