feat(error): Make rx access Error.stack lazily

Error.stack can potentially trigger expensive prepareStackTrace calls,
Observable.timeout would crate a TimeoutError on use, before the actual
error occurs. This eases tracing the location of the timeout, but with
the current implementation, slows down the application when using many
.timeout operators throughout the code.

src/util/ArgumentOutOfRangeError.ts

@@ -9,10 +9,16 @@
  * @class ArgumentOutOfRangeError
  */
 export class ArgumentOutOfRangeError extends Error {
+  private err: Error;
+
   constructor() {
     const err: any = super('argument out of range');
+    this.err = err;
     (<any> this).name = err.name = 'ArgumentOutOfRangeError';
-    (<any> this).stack = err.stack;
     (<any> this).message = err.message;
   }
+
+  get stack() {
+    return this.err.stack;
+  }
 }

src/util/EmptyError.ts

@@ -9,10 +9,16 @@
  * @class EmptyError
  */
 export class EmptyError extends Error {
+  private err: Error;
+
   constructor() {
     const err: any = super('no elements in sequence');
+    this.err = err;
     (<any> this).name = err.name = 'EmptyError';
-    (<any> this).stack = err.stack;
     (<any> this).message = err.message;
   }
+
+  get stack() {
+    return this.err.stack;
+  }
 }

src/util/ObjectUnsubscribedError.ts

@@ -8,10 +8,16 @@
  * @class ObjectUnsubscribedError
  */
 export class ObjectUnsubscribedError extends Error {
+  private err: Error;
+
   constructor() {
     const err: any = super('object unsubscribed');
+    this.err = err;
     (<any> this).name = err.name = 'ObjectUnsubscribedError';
-    (<any> this).stack = err.stack;
     (<any> this).message = err.message;
   }
+
+  get stack() {
+    return this.err.stack;
+  }
 }

src/util/TimeoutError.ts

@@ -1,15 +1,21 @@
-/**
- * An error thrown when duetime elapses.
- *
- * @see {@link timeout}
- *
- * @class TimeoutError
- */
-export class TimeoutError extends Error {
-  constructor() {
-    const err: any = super('Timeout has occurred');
-    (<any> this).name = err.name = 'TimeoutError';
-    (<any> this).stack = err.stack;
-    (<any> this).message = err.message;
-  }
-}
+/**
+ * An error thrown when duetime elapses.
+ *
+ * @see {@link timeout}
+ *
+ * @class TimeoutError
+ */
+export class TimeoutError extends Error {
+  private err: Error;
+
+  constructor() {
+    const err: any = super('Timeout has occurred');
+    this.err = err;
+    (<any> this).name = err.name = 'TimeoutError';
+    (<any> this).message = err.message;
+  }
+
+  get stack() {
+    return this.err.stack;
+  }
+}