Move existing Mojo JS <--> CPP tests out of webui test harness.

mojo/apps/js/test/js_to_cpp.mojom

Index: mojo/apps/js/test/js_to_cpp.mojom
diff --git a/content/test/data/web_ui_test_mojo_bindings.mojom b/mojo/apps/js/test/js_to_cpp.mojom
similarity index 77%
copy from content/test/data/web_ui_test_mojo_bindings.mojom
copy to mojo/apps/js/test/js_to_cpp.mojom
index 9ffd38529a320397c935a60339094bc5459d1f67..0c96335796da2ad26230c80d711ca57f10ca5227 100644
--- a/content/test/data/web_ui_test_mojo_bindings.mojom
+++ b/mojo/apps/js/test/js_to_cpp.mojom
@@ -1,4 +1,4 @@
-module mojo {
+module js_to_cpp {
 
 // This struct encompasses all of the basic types, so that they
 // may be sent from C++ to JS and back for validation.
@@ -21,14 +21,15 @@ struct EchoArgs {
   string[] string_array;
 };
 
-[Peer=RendererTarget]
-interface BrowserTarget {
+[Peer=JsSide]
+interface CppSide {
+  StartTest();  // Sent to notify that the JS side is now ready.
   PingResponse();
   EchoResponse(EchoArgs arg1, EchoArgs arg2);
 };
 
-[Peer=BrowserTarget]
-interface RendererTarget {
+[Peer=CppSide]
+interface JsSide {
   Ping();
   Echo(EchoArgs arg);
 };