Disable flaky FetchAndEmitMetricsWithExtensions on Win/Linux.

TBR=siggi@chromium.org

Bug: 990148
Change-Id: Ibeda7b1d6628105d59d66d8788e5fb99d04a9221
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1731699Reviewed-by: Sky Malice <skym@chromium.org>
Reviewed-by: Erik Chen <erikchen@chromium.org>
Commit-Queue: Sky Malice <skym@chromium.org>
Cr-Commit-Position: refs/heads/master@{#683400}

chrome/browser/metrics/process_memory_metrics_emitter_browsertest.cc

@@ -546,8 +546,10 @@ IN_PROC_BROWSER_TEST_F(ProcessMemoryMetricsEmitterTest,
   CheckPageInfoUkmMetrics(url, true);
 }
 
+// TODO(https://crbug.com/990148): Re-enable on Win and Linux once not flaky.
 #if BUILDFLAG(ENABLE_EXTENSIONS)
-#if defined(ADDRESS_SANITIZER) || defined(MEMORY_SANITIZER)
+#if defined(ADDRESS_SANITIZER) || defined(MEMORY_SANITIZER) || \
+    defined(OS_WIN) || defined(OS_LINUX)
 #define MAYBE_FetchAndEmitMetricsWithExtensions \
   DISABLED_FetchAndEmitMetricsWithExtensions
 #else