Reland r288013: First cut at "content handling" support in Mojo.

mojo/services/public/interfaces/content_handler/BUILD.gn

Index: mojo/services/public/interfaces/content_handler/BUILD.gn
diff --git a/mojo/services/public/interfaces/navigation/BUILD.gn b/mojo/services/public/interfaces/content_handler/BUILD.gn
similarity index 63%
copy from mojo/services/public/interfaces/navigation/BUILD.gn
copy to mojo/services/public/interfaces/content_handler/BUILD.gn
index 73e057828412703daf1776738671425472e2b2e1..c72cc9a2c917308088f8bb0d654fd875eb548da9 100644
--- a/mojo/services/public/interfaces/navigation/BUILD.gn
+++ b/mojo/services/public/interfaces/content_handler/BUILD.gn
@@ -4,13 +4,14 @@
 
 import("//mojo/public/tools/bindings/mojom.gni")
 
-# GYP version: mojo/mojo_services.gypi:mojo_navigation_bindings
-mojom("navigation") {
+# GYP version: mojo/mojo_services.gypi:mojo_content_handler_bindings
+mojom("content_handler") {
   sources = [
-    "navigation.mojom",
+    "content_handler.mojom",
   ]
 
   deps = [
+    "//mojo/public/interfaces/application",
     "//mojo/services/public/interfaces/network",
   ]
 }