Support responseType property on XMLHttpRequest.

Only default, "" and "text" supported for now. Raising an error otherwise.

apps/tests/http-tests.ts

@@ -616,3 +616,16 @@ export function test_raises_onerror_Event(done) {
     xhr.open("GET", "https://no-such-domain-httpbin.org");
     xhr.send();
 }
+
+export function test_responseType(done) {
+    let xhr = new XMLHttpRequest();
+    xhr.responseType = "";
+    xhr.responseType = "text";
+
+    TKUnit.assertThrows(
+        () => xhr.responseType = "json",
+        "Didn't raise on unsupported type.",
+        "Response type of 'json' not supported."
+    );
+    done(null);
+}

declarations.d.ts

@@ -37,6 +37,7 @@ declare class XMLHttpRequest {
     overrideMimeType(mime: string): void;
     readyState: number;
     responseText: string;
+    responseType: string;
     status: number;
 
     onload: () => void;

http/http.ts

@@ -49,6 +49,7 @@ export class XMLHttpRequest {
     private _responseText: string = "";
     private _headers: any;
     private _errorFlag: boolean;
+    private _responseType: string;
 
     public onreadystatechange: Function;
 
@@ -163,6 +164,18 @@ export class XMLHttpRequest {
         return this._readyState;
     }
 
+    public get responseType(): string {
+        return this._responseType;
+    }
+
+    public set responseType(value: string) {
+        if (value === "" || value === "text") {
+            this._responseType = value;
+        } else {
+            throw new Error(`Response type of '${value}' not supported.`);
+        }
+    }
+
     private _setReadyState(value: number) {
         if (this._readyState !== value) {
             this._readyState = value;