fix(AjaxObservable): catch XHR send failures to observer

spec/observables/dom/ajax-spec.ts

@@ -177,6 +177,33 @@ describe('Observable.ajax', () => {
     expect(error).to.be.an('error', 'wokka wokka');
   });
 
+  it('should error if send request throws', (done: MochaDone) => {
+    const expected = new Error('xhr send failure');
+
+    const obj = {
+      url: '/flibbertyJibbet',
+      responseType: 'text',
+      method: '',
+      createXHR: () => {
+        const ret = new MockXMLHttpRequest();
+        ret.send = () => {
+          throw expected;
+        };
+        return ret as any;
+      }
+    };
+
+    Rx.Observable.ajax(obj)
+      .subscribe(() => {
+        done(new Error('should not be called'));
+      }, (e: Error) => {
+        expect(e).to.be.equal(expected);
+        done();
+      }, () => {
+        done(new Error('should not be called'));
+      });
+  });
+
   it('should succeed on 200', () => {
     const expected = { foo: 'bar' };
     let result;
@@ -410,6 +437,34 @@ describe('Observable.ajax', () => {
       expect(MockXMLHttpRequest.mostRecent.url).to.equal('/flibbertyJibbet');
       expect(MockXMLHttpRequest.mostRecent.data).to.equal('{"🌟":"🚀"}');
     });
+
+    it('should error if send request throws', (done: MochaDone) => {
+      const expected = new Error('xhr send failure');
+
+      const obj = {
+        url: '/flibbertyJibbet',
+        responseType: 'text',
+        method: '',
+        body: 'foobar',
+        createXHR: () => {
+          const ret = new MockXMLHttpRequest();
+          ret.send = () => {
+            throw expected;
+          };
+          return ret as any;
+        }
+      };
+
+      Rx.Observable.ajax(obj)
+        .subscribe(() => {
+          done(new Error('should not be called'));
+        }, (e: Error) => {
+          expect(e).to.be.equal(expected);
+          done();
+        }, () => {
+          done(new Error('should not be called'));
+        });
+    });
   });
 
   describe('ajax.get', () => {

src/observable/dom/AjaxObservable.ts

@@ -248,10 +248,10 @@ export class AjaxSubscriber<T> extends Subscriber<Event> {
       this.setupEvents(xhr, request);
 
       // finally send the request
-      if (body) {
-        xhr.send(body);
-      } else {
-        xhr.send();
+      result = body ? tryCatch(xhr.send).call(xhr, body) : tryCatch(xhr.send).call(xhr);
+      if (result === errorObject) {
+        this.error(errorObject.e);
+        return null;
       }
     }