Add fuzz executable to GN

BUILD.gn

Index: BUILD.gn
diff --git a/BUILD.gn b/BUILD.gn
index 3a81d369ae880e028034ea8521f45eca3802a185..b8ddbf9927398bdeeed1ac7c58994a5da5ec1b53 100644
--- a/BUILD.gn
+++ b/BUILD.gn
@@ -987,4 +987,27 @@ if (skia_enable_tools) {
     ]
     testonly = true
   }
+
+  executable("fuzz") {
+    sources = [
+      "fuzz/FilterFuzz.cpp",
+      "fuzz/FuzzGradients.cpp",
+      "fuzz/FuzzParsePath.cpp",
+      "fuzz/FuzzPathop.cpp",
+      "fuzz/FuzzScaleToSides.cpp",
+      "fuzz/fuzz.cpp",
+    ]
+    deps = [
+      ":common_flags",
+      ":experimental_svg_model",
+      ":flags",
+      ":gm",
+      ":gpu_tool_utils",
+      ":skia",
+      ":tool_utils",
+      "//third_party/jsoncpp",
+      "//third_party/libpng",
+    ]
+    testonly = true
+  }
 }