iron-ajax sends invalid JSON body if it's a string

[Boscop]

When I use <iron-ajax> with content-type="application/json" (and method="post") and then I do this:

        this.$.xhr.body = "foo";
        this.$.xhr.generateRequest();

it just sends foo as the body of the request, but it should send "foo".
A string like "foo" is a valid JSON object but foo is not!

[terrak]

I think your body should be an object :
this.$.xhr.body = {myvar:"foo"};
or
this.$.xhr.body = JSON.stringify( {myvar:"foo"} );

[drix]

you can do

this.$.xhr.body = '"foo"';
this.$.xhr.generateRequest();

Any change to stringify a body string would slow iron-request performance a bit because it would have to check if the string is just a string or a json stringified otherwise:
this.$.xhr.body = JSON.stringify( {myvar:"foo"} );
would generate an invalid outcome.

I vote to this issue be resolved with some info about this behavior been add to the documentation.