Exclude inherited Error properties from stack trace

These are likely to be methods or other things that aren't meaningful in
Jasmine's output.

spec/core/ExceptionFormatterSpec.js

@@ -197,7 +197,7 @@ describe('ExceptionFormatter', function() {
       expect(new jasmineUnderTest.ExceptionFormatter().stack()).toBeNull();
     });
 
-    it('includes error properties in stack', function() {
+    it("includes the error's own properties in stack", function() {
       const error = new Error('an error');
       error.someProperty = 'hello there';
 
@@ -206,6 +206,19 @@ describe('ExceptionFormatter', function() {
       expect(result).toMatch(/error properties:.*someProperty.*hello there/);
     });
 
+    it('does not include inherited error properties', function() {
+      function CustomError(msg) {
+        Error.call(this, msg);
+      }
+
+      CustomError.prototype = new Error();
+      CustomError.prototype.anInheritedProp = 'something';
+      const error = new CustomError('nope');
+
+      const result = new jasmineUnderTest.ExceptionFormatter().stack(error);
+      expect(result).not.toContain('anInheritedProp');
+    });
+
     describe('When omitMessage is true', function() {
       it('filters the message from V8-style stack traces', function() {
         const error = {

src/core/ExceptionFormatter.js

@@ -102,7 +102,7 @@ getJasmineRequireObj().ExceptionFormatter = function(j$) {
       const result = {};
       let empty = true;
 
-      for (const prop in error) {
+      for (const prop of Object.keys(error)) {
         if (ignoredProperties.includes(prop)) {
           continue;
         }