Start work on adding content/browser to GN build.

content/public/common/BUILD.gn

Index: content/public/common/BUILD.gn
diff --git a/content/public/common/BUILD.gn b/content/public/common/BUILD.gn
index 8bef0b6f2fab295c68a6cb6f9dbd34bf189660bd..32fd84e09d57ec3ee21d1efec879fd22ed3b89a9 100644
--- a/content/public/common/BUILD.gn
+++ b/content/public/common/BUILD.gn
@@ -10,13 +10,11 @@ source_set("common") {
 
   configs += [
     "//content:content_implementation",
-    # TODO(GYP) remove when blink_headers target is converted.
-    "//content:blink_headers_stub_config",
   ]
 
   deps = [
     "//content/common",
     "//skia",
-    #"//third_party/WebKit/public:blink_headers",
+    "//third_party/WebKit/public:blink_headers",
   ]
 }