Colormatrix GPU fix with saturated alpha.

src/effects/SkColorMatrixFilter.cpp

Index: src/effects/SkColorMatrixFilter.cpp
diff --git a/src/effects/SkColorMatrixFilter.cpp b/src/effects/SkColorMatrixFilter.cpp
index bb85485050813e776aa1ecd6489819cbc5aef79c..23be874b97121ef0f17667475d77b4471c33ecb9 100644
--- a/src/effects/SkColorMatrixFilter.cpp
+++ b/src/effects/SkColorMatrixFilter.cpp
@@ -424,6 +424,7 @@ public:
                                    builder->getUniformCStr(fMatrixHandle),
                                    inputColor,
                                    builder->getUniformCStr(fVectorHandle));
+            builder->fsCodeAppendf("\t%s = clamp(%s, 0.0, 1.0);\n", outputColor, outputColor);
             builder->fsCodeAppendf("\t%s.rgb *= %s.a;\n", outputColor, outputColor);
         }