Change all GCs in internals-observe-gc.html to precise GC

Change all GCs in internals-observe-gc.html to precise GC in an attempt to fix the failures on Win7 bot.

Bug: 1011714
Change-Id: Ie9c101b01b3ca28dc87c927ddc2cf73eec1b991e
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1844525Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Commit-Queue: Keishi Hattori <keishi@chromium.org>
Cr-Commit-Position: refs/heads/master@{#703277}

third_party/blink/web_tests/fast/harness/internals-observe-gc.html

@@ -27,7 +27,7 @@ var valueA, observationA, observationB, observationC;
     observationA = internals.observeGC(valueA);
   })();
 
-  gc();
+  await runAsyncGC();
   shouldBeFalse('observationA.wasCollected');
   // value ineligible for GC should not be flagged as collected
   valueA = null;
@@ -43,7 +43,7 @@ var valueA, observationA, observationB, observationC;
     observationB = internals.observeGC(valueB);
   })();
 
-  gc();
+  await runAsyncGC();
   shouldBeTrue('observationB.wasCollected');
   // value eligible for GC should be flagged as collected
   observationB = null;
@@ -83,7 +83,7 @@ var valueA, observationA, observationB, observationC;
     observerD.observed = valueD;
   })();
 
-  gc();
+  await runAsyncGC();
   testPassed('did not crash');
 
   finishJSTest();