Add some simple HTMLViewer apptests.

BUILD.gn

Index: BUILD.gn
diff --git a/BUILD.gn b/BUILD.gn
index a8000b63e729c0b1fcf0d226801c64f016395344..7fe51cef1fce74971d43fcea2ae45aa0c7ad7376 100644
--- a/BUILD.gn
+++ b/BUILD.gn
@@ -576,12 +576,13 @@ group("gn_mojo_targets") {
       "//third_party/mojo_services/src/window_manager/public/interfaces:interfaces_python",
     ]
 
-    if (!is_debug) {

[sky, 2015/04/02 16:56:17]

Wow, this is weird. I wonder why we had these two in only release mode?

+    #if (!is_debug) {
       deps += [
         "//mojo/services/html_viewer:tests",
+        "//mojo/services/html_viewer:apptests",
         "//mojo/services/network:apptests",
       ]
-    }
+    #}
   }
 }