Add the 'lighter' composite operation to feComposite.

Source/platform/graphics/filters/FEComposite.cpp

Index: Source/platform/graphics/filters/FEComposite.cpp
diff --git a/Source/platform/graphics/filters/FEComposite.cpp b/Source/platform/graphics/filters/FEComposite.cpp
index 066a66b6eb7590bb0d80625f0d6dad2193c15391..bb89b5c8cf1ad4d88d2b35f13f2b7889c2bad6ce 100644
--- a/Source/platform/graphics/filters/FEComposite.cpp
+++ b/Source/platform/graphics/filters/FEComposite.cpp
@@ -184,6 +184,8 @@ SkXfermode::Mode toXfermode(CompositeOperationType mode)
         return SkXfermode::kSrcATop_Mode;
     case FECOMPOSITE_OPERATOR_XOR:
         return SkXfermode::kXor_Mode;
+    case FECOMPOSITE_OPERATOR_LIGHTER:
+        return SkXfermode::kPlus_Mode;
     default:
         ASSERT_NOT_REACHED();
         return SkXfermode::kSrcOver_Mode;
@@ -237,6 +239,9 @@ static TextStream& operator<<(TextStream& ts, const CompositeOperationType& type
     case FECOMPOSITE_OPERATOR_ARITHMETIC:
         ts << "ARITHMETIC";
         break;
+    case FECOMPOSITE_OPERATOR_LIGHTER:
+        ts << "LIGHTER";
+        break;
     }
     return ts;
 }