Pass ResizeObserver as 'this' to callback

third_party/WebKit/LayoutTests/resize-observer/observe.html

Index: third_party/WebKit/LayoutTests/resize-observer/observe.html
diff --git a/third_party/WebKit/LayoutTests/resize-observer/observe.html b/third_party/WebKit/LayoutTests/resize-observer/observe.html
index 3a47d30bc7ca2b4e2cc114e4141f7fddd02fb384..ea3bc6f7448c1bfa5b3429fb828dd344ac31f0cc 100644
--- a/third_party/WebKit/LayoutTests/resize-observer/observe.html
+++ b/third_party/WebKit/LayoutTests/resize-observer/observe.html
@@ -164,6 +164,29 @@ function test6() {
   return promise;
 }
 
+function test7() {
+  let harnessTest = async_test("test7: callback.this");
+  let resolvePromise;
+  let ro = new ResizeObserver( function(entries, obs)  {
+    let callbackThis = this;
+    resolvePromise();
+    harnessTest.step(() => {
+      assert_equals(callbackThis, ro, "callback.this is ResizeObserver");
+      assert_equals(obs, ro, "2nd argument is ResizeObserver");
+      ro.disconnect();
+      ro = null;  // must null every reference to RO to prevent leaks

[eae, 2016/09/05 20:52:48]

Is this documented anywhere?

[esprehn, 2016/09/06 01:35:30]

Yeah that doesn't seem right, you shouldn't need to null anything. What's
leaking here?

[esprehn, 2016/09/06 01:35:31]

Yeah that doesn't seem right, you shouldn't need to null anything. What's
leaking here?

[atotic1, 2016/09/06 17:22:37]

This is only required to pass run-webkit-tests --enable-leak-detection
I have no proof, since leak detector does not report what has leaked. This
is what I believe is happening:
- leak-detection runs on harnessTest.done().
- leak-detection reports a leak if ResizeObserver is alive when it runs.
- all the references from JS to ResizeObserver must be cleared for
ResizeObserver to be GCd
- therefore, all references from JS to ResizeObserver must be set to null before
test is done.

My other tests also null ResizeObserver before calling done, but this is done by
test framework in ResizeTestHelper._done.

[haraken, 2016/09/07 01:59:45]

Ah, this makes sense. It's totally valid a thing that the underlying DOM object
is kept alive while the JS wrapper is alive.

This is not a leak. Reword the comment at line 177.

+      callbackThis = null;
+      obs = null;
+      harnessTest.done();
+     });
+    }
+  );
+  ro.observe(t1);
+
+  return new Promise( (resolve, reject) => {
+    resolvePromise = resolve;
+  });
+}
 let guard = async_test('guard');
 test0()
   .then(() => { return test1(); })
@@ -172,6 +195,7 @@ test0()
   .then(() => { return test4(); })
   .then(() => { return test5(); })
   .then(() => { return test6(); })
+  .then(() => { return test7(); })
   .then(() => { guard.done(); });
 
 </script>