Add toJSON to some performance idls

This CL adds toJSON to the following:
* PerformanceLongTaskTiming
* PerformanceResourceTiming
* TaskAttributionTiming
* Performance within workers

Link to Intent to Implement and Ship thread:
https://groups.google.com/a/chromium.org/forum/#!topic/blink-dev/ZnXvNe_wNyk

Bug: 740094
Change-Id: I54622b9bd213fd806a9108598ccf4798c2ceffa2
Reviewed-on: https://chromium-review.googlesource.com/802019
Reviewed-by: Jeremy Roman <jbroman@chromium.org>
Reviewed-by: Philip Jägenstedt <foolip@chromium.org>
Reviewed-by: Bo <boliu@chromium.org>
Reviewed-by: Timothy Dresser <tdresser@chromium.org>
Commit-Queue: Nicolás Peña Moreno <npm@chromium.org>
Cr-Commit-Position: refs/heads/master@{#523532}
diff --git a/workers/worker-performance.worker.js b/workers/worker-performance.worker.js
index c4e562b..88db976 100644
--- a/workers/worker-performance.worker.js
+++ b/workers/worker-performance.worker.js
@@ -110,9 +110,9 @@
     assert_equals(typeof(performance.navigation), "undefined", "performance.navigation is undefined");
 }, "performance.navigation is not available in workers");
 
-test(function testPerformanceHasNoToJSON () {
-    assert_equals(typeof(performance.toJSON), "undefined", "performance.toJSON is undefined");
-}, "performance.toJSON is not available in workers");
+test(function testPerformanceHasToJSON () {
+    assert_equals(typeof(performance.toJSON), "function", "performance.toJSON is a function");
+}, "performance.toJSON is available in workers");
 
 test(function testPerformanceNoNavigationEntries () {
     assert_equals(performance.getEntriesByType("navigation").length, 0, "getEntriesByType(\"navigation\") returns nothing");