cppgc: Increase tolerance in MetricRecorder unittests

Tolerance was set to 50 microseconds. This is not enough and causes
flaky failures. Tolerance is needed because we record milliseconds and
an empty scope can still take a few milliseconds to create and destroy.

Increasing the tolerance to 500 microseconds should suffice and makes
sense for the test. All expected values are in 10s of milliseconds, so
half a millisecond tolerance should be reasonable.

Bug: v8:11367
Change-Id: I2d284efe5176ec9938b6a378f4b5f1bda0e58781
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2659058
Commit-Queue: Omer Katz <omerkatz@chromium.org>
Auto-Submit: Omer Katz <omerkatz@chromium.org>
Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Cr-Commit-Position: refs/heads/master@{#72426}

test/unittests/heap/cppgc/metric-recorder-unittest.cc

@@ -201,7 +201,7 @@ TEST_F(MetricRecorderTest, CycleEndHistogramReportsCorrectValues) {
   }
   EndGC(300);
   // Check durations.
-  static constexpr int64_t kDurationComparisonTolerance = 50;
+  static constexpr int64_t kDurationComparisonTolerance = 500;
   EXPECT_LT(std::abs(MetricRecorderImpl::CppGCFullCycle_event
                          .main_thread_incremental.mark_duration_us -
                      10000),