Get mojo_shell building inside chromium checkout.

mojo/application/BUILD.gn

Index: mojo/application/BUILD.gn
diff --git a/mojo/application/BUILD.gn b/mojo/application/BUILD.gn
index dda877ea9daf029c747cbf0fc1d89d81b7417da0..0087ebcf95ff46e49ede269a9e46acbd826ea1ef 100644
--- a/mojo/application/BUILD.gn
+++ b/mojo/application/BUILD.gn
@@ -19,6 +19,22 @@ source_set("application") {
   ]
 }
 
+source_set("content_handler") {
+  sources = [
+    "content_handler_factory.cc",
+    "content_handler_factory.h",
+  ]
+  deps = [
+    ":application",
+    "//base",
+    "//mojo/common",
+    "//mojo/environment:chromium",
+    "//third_party/mojo/src/mojo/public/interfaces/application",
+    "//third_party/mojo_services/src/content_handler/public/interfaces",
+    "//mojo/services/network/public/interfaces",
+  ]
+}
+
 source_set("test_support") {
   testonly = true
   sources = [