cc: Fix a bug where filter outsets for drop-shadow could be negative.

cc/output/filter_operations.cc

Index: cc/output/filter_operations.cc
diff --git a/cc/output/filter_operations.cc b/cc/output/filter_operations.cc
index 8263518640b8a30f291febaba75dd92684e215aa..f0cca86f744548c58b57bf238c1d0dccb37c27f9 100644
--- a/cc/output/filter_operations.cc
+++ b/cc/output/filter_operations.cc
@@ -110,10 +110,10 @@ void FilterOperations::GetOutsets(int* top,
           *bottom += spread;
           *left += spread;
         } else {
-          *top += spread - op.drop_shadow_offset().y();
-          *right += spread + op.drop_shadow_offset().x();
-          *bottom += spread + op.drop_shadow_offset().y();
-          *left += spread - op.drop_shadow_offset().x();
+          *top += std::max(0, spread - op.drop_shadow_offset().y());

[enne (OOO), 2016/07/06 17:34:57]

What if your drop shadow is up and to the left instead of down and to the right?
Does (-3, -8) really have the same outsets as (3, 8)?

[jbroman, 2016/07/06 17:37:32]

I don't understand your question. No, it doesn't have the same outsets; it has
opposite outsets. For example, in the test below, the outsets for (-3, -8) would
be top=8, right=0, bottom=0, left=3.

This isn't std::abs(x); it's std::max(0, x). It only ensures that no edge gets
negative outsets.

[enne (OOO), 2016/07/06 17:57:18]

*drinks more coffee* Oops, sorry about misreading that.

+          *right += std::max(0, spread + op.drop_shadow_offset().x());
+          *bottom += std::max(0, spread + op.drop_shadow_offset().y());
+          *left += std::max(0, spread - op.drop_shadow_offset().x());
         }
       }
     }