AW UMA: fix a minor test bug

No change to production logic.

This fixes a bug in aw_metrics_service_client_unittest.cc. SetInSample()
should have changed IsInSample()'s return value, but it didn't. This
fixes that.

Tests are still passing with and without this change.

Fixed: 1020780
Test: run_android_webview_unittests --gtest_filter=AwMetricsServiceClientTest.*
Change-Id: Id2061d6cf80129cfa1dfb29a869e185615526fd4
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1895900
Auto-Submit: Nate Fischer <ntfschr@chromium.org>
Commit-Queue: Shimi Zhang <ctzsm@chromium.org>
Reviewed-by: Shimi Zhang <ctzsm@chromium.org>
Cr-Commit-Position: refs/heads/master@{#712175}

android_webview/browser/metrics/aw_metrics_service_client_unittest.cc

@@ -38,7 +38,7 @@ class TestClient : public AwMetricsServiceClient {
   void SetInSample(bool value) { in_sample_ = value; }
 
  protected:
-  bool IsInSample() override { return true; }
+  bool IsInSample() override { return in_sample_; }
 
  private:
   bool in_sample_;