perf(skipWhile): remove tryCatch/errorObject (~1.6x improvement)

Before:
                      |      RxJS 4.0.7 | RxJS 5.0.0-beta.1 | factor | % improved
----------------------------------------------------------------------------------
skipwhile - immediate | 27,101 (±1.37%) |  122,827 (±0.29%) |  4.53x |     353.2%
            skipwhile |  8,034 (±1.32%) |   82,160 (±0.28%) | 10.23x |     922.7%

After:
                      |      RxJS 4.0.7 | RxJS 5.0.0-beta.1 | factor | % improved
----------------------------------------------------------------------------------
skipwhile - immediate | 27,040 (±0.30%) |  197,417 (±0.28%) |  7.30x |     630.1%
            skipwhile |  8,842 (±2.08%) |  112,757 (±0.55%) | 12.75x |   1,175.2%

src/operator/skipWhile.ts

@@ -1,8 +1,6 @@
 import {Observable} from '../Observable';
 import {Operator} from '../Operator';
 import {Subscriber} from '../Subscriber';
-import {tryCatch} from '../util/tryCatch';
-import {errorObject} from '../util/errorObject';
 
 /**
  * Returns an Observable that skips all items emitted by the source Observable as long as a specified condition holds
@@ -38,17 +36,21 @@ class SkipWhileSubscriber<T> extends Subscriber<T> {
 
   protected _next(value: T): void {
     const destination = this.destination;
-    if (this.skipping === true) {
-      const index = this.index++;
-      const result = tryCatch(this.predicate)(value, index);
-      if (result === errorObject) {
-        destination.error(errorObject.e);
-      } else {
-        this.skipping = Boolean(result);
-      }
+    if (this.skipping) {
+      this.tryCallPredicate(value);
     }
-    if (this.skipping === false) {
+
+    if (!this.skipping) {
       destination.next(value);
     }
   }
+
+  private tryCallPredicate(value: T): void {
+    try {
+      const result = this.predicate(value, this.index++);
+      this.skipping = Boolean(result);
+    } catch (err) {
+      this.destination.error(err);
+    }
+  }
 }