Mojo: Add String, Float, and Double types to codec.js.

content/test/data/web_ui_test_mojo_bindings.mojom

 module mojo {
 
 // This struct encompasses all of the basic types, so that they
 // may be sent from C++ to JS and back for validation.
 struct EchoArgs {
   int64 si64;
   int32 si32;
   int16 si16;
   int8  si8;
   uint64 ui64;
   uint32 ui32;
   uint16 ui16;
   uint8  ui8;
   float float_val;
   float float_inf;
   float float_nan;
   double double_val;
   double double_inf;
   double double_nan;
   string name;
+  string[] string_array;
 };
 
 [Peer=RendererTarget]
 interface BrowserTarget {
   PingResponse();
   EchoResponse(EchoArgs arg1, EchoArgs arg2);
 };
 
 [Peer=BrowserTarget]
 interface RendererTarget {
   Ping();
   Echo(EchoArgs arg);
 };
 
 }