Revert of Content "gn check" work.

.gn

Index: .gn
diff --git a/.gn b/.gn
index d851064f43c8470b95e947e23354f0c6afc0e45c..f7ebb4167c5e8e1e424c174cf032dc9552a9e666 100644
--- a/.gn
+++ b/.gn
@@ -36,21 +36,8 @@
   "//components/*",
 
   #"//content/*",  # A whole lot of errors.
-  "//content/gpu/*",
-  "//content/plugin/*",
   "//content/public/*",
   "//content/renderer/*",
-
-  #"//content/shell/*",  # Needs Android fix, bug 597020.
-
-  #"//content/test/*",  # A couple of errors left.
-  "//content/test:content_gl_benchmark",
-  "//content/test:content_gl_tests",
-  "//content/test:content_perftests",
-  "//content/test:content_site_isolation_browsertests",
-  "//content/test:content_test_mojo_bindings",
-  "//content/test:content_unittests",
-  "//content/test:test_support",
   "//courgette/*",
   "//crypto/*",
   "//data/*",