Allow for hint cache to stabilize before loading hints after browser wipe

Bug: 1166906
Change-Id: I29b4ffd8e91923e0e86dc4b7fa6a0f54f0e4f63f
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2631745Reviewed-by: Michael Crouse <mcrouse@chromium.org>
Commit-Queue: Sophie Chang <sophiechang@chromium.org>
Cr-Commit-Position: refs/heads/master@{#843960}

chrome/browser/optimization_guide/hints_fetcher_browsertest.cc

@@ -792,15 +792,6 @@ IN_PROC_BROWSER_TEST_F(
       1, 1);
 }
 
-// TODO(crbug.com/1166906):
-// HintsFetcherBrowserTest.HintsFetcherClearFetchedHints is flaky on Windows and
-// Linux.
-#if defined(OS_WIN) || defined(OS_LINUX)
-#define MAYBE_HintsFetcherClearFetchedHints \
-  DISABLED_HintsFetcherClearFetchedHints
-#else
-#define MAYBE_HintsFetcherClearFetchedHints HintsFetcherClearFetchedHints
-#endif  // defined(OS_WIN) || defined(OS_LINUX)
 IN_PROC_BROWSER_TEST_F(HintsFetcherBrowserTest, HintsFetcherClearFetchedHints) {
   const base::HistogramTester* histogram_tester = GetHistogramTester();
   GURL url = https_url();
@@ -836,6 +827,10 @@ IN_PROC_BROWSER_TEST_F(HintsFetcherBrowserTest, HintsFetcherClearFetchedHints) {
   // Wipe the browser history - clear all the fetched hints.
   browser()->profile()->Wipe();
 
+  // Wait until hint cache stabilizes and clears all the fetched hints.
+  base::ThreadPoolInstance::Get()->FlushForTesting();
+  base::RunLoop().RunUntilIdle();
+
   // Try to load the same hint to confirm fetched hints are no longer there.
   LoadHintsForUrl(https_url());