Make GN's "check" run cleanly.

skia/BUILD.gn

Index: skia/BUILD.gn
diff --git a/skia/BUILD.gn b/skia/BUILD.gn
index 04919bf2a45b3fb6964e4f18575e2fec6ca394f4..f65b2cc2394459f5a09cf7d7f8ccb488ae198123 100644
--- a/skia/BUILD.gn
+++ b/skia/BUILD.gn
@@ -371,6 +371,10 @@ source_set("skia_opts") {
 
       # Chrome-specific.
       "ext/convolver_SSE2.cc",
+
+      # These are header files used by this target from the skia one above.
+      "ext/convolver.h",
+      "//third_party/skia/include/core/SkTypes.h",
     ]
 
     if (is_linux || is_mac) {
@@ -386,6 +390,9 @@ source_set("skia_opts") {
     "//build/config/compiler:no_chromium_code"
   ]
 
-  # TODO(brettw) uncomment when visibility is supported.
-  #visibility = ":skia"
+  deps = [
+    "//base",
+  ]
+
+  visibility = ":skia"
 }