Restructure public side of navigation service.

This CL goes from this:
  //mojo/services/public/interfaces/navigation

to this:
  //mojo/services/navigation/public/interfaces

This CL also makes the Mojo-side changes necessary to roll this change into
Chromium.

TBR=beng

Review URL: https://codereview.chromium.org/796783002

engine/src/flutter/tools/debugger/BUILD.gn

@@ -31,7 +31,7 @@ mojo_native_application("sky_debugger") {
     "//mojo/public/cpp/bindings",
     "//mojo/public/cpp/utility",
     "//mojo/services/input_events/public/interfaces",
-    "//mojo/services/public/interfaces/navigation",
+    "//mojo/services/navigation/public/interfaces",
     "//mojo/services/view_manager/public/cpp",
     "//services/window_manager:lib",
     "//sky/viewer:bindings",

engine/src/flutter/tools/debugger/debugger.h

@@ -8,7 +8,7 @@
 #include "mojo/public/cpp/application/connect.h"
 #include "mojo/public/cpp/application/service_provider_impl.h"
 #include "mojo/services/input_events/public/interfaces/input_events.mojom.h"
-#include "mojo/services/public/interfaces/navigation/navigation.mojom.h"
+#include "mojo/services/navigation/public/interfaces/navigation.mojom.h"
 #include "mojo/services/view_manager/public/cpp/view_manager.h"
 #include "mojo/services/view_manager/public/cpp/view_manager_delegate.h"
 #include "mojo/services/view_manager/public/cpp/view_observer.h"

engine/src/flutter/tools/debugger/navigator_host_impl.h

@@ -7,7 +7,7 @@
 
 #include "base/memory/weak_ptr.h"
 #include "mojo/public/cpp/application/interface_factory_impl.h"
-#include "mojo/services/public/interfaces/navigation/navigation.mojom.h"
+#include "mojo/services/navigation/public/interfaces/navigation.mojom.h"
 #include "sky/tools/debugger/debugger.mojom.h"
 
 namespace sky {