Add content/child to the GN build.

content/public/child/BUILD.gn

Index: content/public/child/BUILD.gn
diff --git a/content/public/common/BUILD.gn b/content/public/child/BUILD.gn
similarity index 56%
copy from content/public/common/BUILD.gn
copy to content/public/child/BUILD.gn
index 32fd84e09d57ec3ee21d1efec879fd22ed3b89a9..93b3f193751928d1b33ec24ed3c29c2f0244ffa4 100644
--- a/content/public/common/BUILD.gn
+++ b/content/public/child/BUILD.gn
@@ -1,20 +1,18 @@
-# Copyright 2014 The Chromium Authors. All rights reserved.
-# Use of this source code is governed by a BSD-style license that can be
-# found in the LICENSE file.
-
-import("//content/common/common.gni")
-
-source_set("common") {
-  sources = rebase_path(content_common_gypi_values.public_common_sources,
-                        ".", "//content")
-
-  configs += [
-    "//content:content_implementation",
-  ]
-
-  deps = [
-    "//content/common",
-    "//skia",
-    "//third_party/WebKit/public:blink_headers",
-  ]
-}
+# Copyright 2014 The Chromium Authors. All rights reserved.
+# Use of this source code is governed by a BSD-style license that can be
+# found in the LICENSE file.
+
+import("//content/child/child.gni")
+
+source_set("child") {
+  sources = rebase_path(content_child_gypi_values.public_child_sources,
+                        ".", "//content")
+
+  configs += [
+    "//content:content_implementation",
+  ]
+
+  deps = [
+    "//content/child",
+  ]
+}