cc: Changed ComputeExpansionDelta to never return a delta less than zero

cc/resources/picture_layer_tiling.cc

 // Copyright 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 "cc/resources/picture_layer_tiling.h"
 
 #include <algorithm>
 #include <cmath>
 #include <limits>
 #include <set>
@@ skipping 805 matching lines @@
 int ComputeExpansionDelta(int num_x_edges, int num_y_edges,
                           int width, int height,
                           int64 target_area) {
   // Compute coefficients for the quadratic equation:
   //   a*x^2 + b*x + c = 0
   int a = num_y_edges * num_x_edges;
   int b = num_y_edges * width + num_x_edges * height;
   int64 c = static_cast<int64>(width) * height - target_area;
 
   // Compute the delta for our edges using the quadratic equation.
-  return a == 0 ? -c / b :
-     (-b + static_cast<int>(
-         std::sqrt(static_cast<int64>(b) * b - 4.0 * a * c))) / (2 * a);
+  int delta =
+      (a == 0) ? -c / b : (-b + static_cast<int>(std::sqrt(
+                                    static_cast<int64>(b) * b - 4.0 * a * c))) /
+                              (2 * a);
+  return std::max(0, delta);
 }
 
 }  // namespace
 
 gfx::Rect PictureLayerTiling::ExpandRectEquallyToAreaBoundedBy(
     const gfx::Rect& starting_rect,
     int64 target_area,
     const gfx::Rect& bounding_rect,
     RectExpansionCache* cache) {
   if (starting_rect.IsEmpty())
@@ skipping 359 matching lines @@
   DCHECK(*this);
   do {
     ++current_eviction_tiles_index_;
   } while (current_eviction_tiles_index_ != eviction_tiles_->size() &&
            !(*eviction_tiles_)[current_eviction_tiles_index_]->HasResources());
 
   return *this;
 }
 
 }  // namespace cc