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

cc/resources/picture_layer_tiling.cc

Index: cc/resources/picture_layer_tiling.cc
diff --git a/cc/resources/picture_layer_tiling.cc b/cc/resources/picture_layer_tiling.cc
index 8cb342488e8cc6505f97764a7c7d9eff10be92ae..0d50658061e0ed0e3b015e4d54980d9b9b38fc49 100644
--- a/cc/resources/picture_layer_tiling.cc
+++ b/cc/resources/picture_layer_tiling.cc
@@ -823,9 +823,11 @@ int ComputeExpansionDelta(int num_x_edges, int num_y_edges,
   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