perf(switchMapTo): remove tryCatch/errorObject (~2x improvement)

Before:
                                       |     RxJS 4.0.7 | RxJS 5.0.0-beta.1 | factor | % improved
--------------------------------------------------------------------------------------------------
switchmapto-resultselector - immediate | 1,695 (±1.02%) |   12,229 (±1.15%) |  7.21x |     621.3%
               switchmapto - immediate | 2,910 (±0.80%) |   32,560 (±0.99%) | 11.19x |   1,018.8%
            switchmapto-resultselector | 2,621 (±0.87%) |   12,473 (±0.49%) |  4.76x |     375.9%
                           switchmapto | 3,300 (±2.11%) |   15,433 (±0.57%) |  4.68x |     367.7%

After:
                                       |     RxJS 4.0.7 | RxJS 5.0.0-beta.1 | factor | % improved
--------------------------------------------------------------------------------------------------
switchmapto-resultselector - immediate | 1,645 (±2.07%) |   28,788 (±5.21%) | 17.50x |   1,650.5%
               switchmapto - immediate | 3,056 (±0.65%) |   31,656 (±1.17%) | 10.36x |     936.0%
            switchmapto-resultselector | 2,793 (±0.54%) |   14,322 (±1.15%) |  5.13x |     412.7%
                           switchmapto | 3,381 (±4.13%) |   15,969 (±3.86%) |  4.72x |     372.2%

Author: luisgabriel

src/operator/switchMapTo.ts

@@ -2,8 +2,6 @@ import {Operator} from '../Operator';
 import {Observable} from '../Observable';
 import {Subscriber} from '../Subscriber';
 import {Subscription} from '../Subscription';
-import {tryCatch} from '../util/tryCatch';
-import {errorObject} from '../util/errorObject';
 import {OuterSubscriber} from '../OuterSubscriber';
 import {InnerSubscriber} from '../InnerSubscriber';
 import {subscribeToResult} from '../util/subscribeToResult';
@@ -69,14 +67,23 @@ class SwitchMapToSubscriber<T, R, R2> extends OuterSubscriber<T, R> {
              innerSub: InnerSubscriber<T, R>): void {
     const { resultSelector, destination } = this;
     if (resultSelector) {
-      const result = tryCatch(resultSelector)(outerValue, innerValue, outerIndex, innerIndex);
-      if (result === errorObject) {
-        destination.error(errorObject.e);
-      } else {
-        destination.next(result);
-      }
+      this.tryResultSelector(outerValue, innerValue, outerIndex, innerIndex);
     } else {
       destination.next(innerValue);
     }
   }
+
+  private tryResultSelector(outerValue: T, innerValue: R,
+                            outerIndex: number, innerIndex: number): void {
+    const { resultSelector, destination } = this;
+    let result: R2;
+    try {
+      result = resultSelector(outerValue, innerValue, outerIndex, innerIndex);
+    } catch (err) {
+      destination.error(err);
+      return;
+    }
+
+    destination.next(result);
+  }
 }