Sync: Disable SearchProviderTest.SendsWarmUpRequestOnFocus on TSan.

The test is flaky on Linux TSan builder.

Example:
https://ci.chromium.org/p/chromium/builders/luci.chromium.ci/Linux%20TSan%20Tests/26934

TBR=jdonnelly@chromium.org

Bug: 891959
Change-Id: Ia29f4d01145588f97a6e34b1e1fa833186238dfb
Reviewed-on: https://chromium-review.googlesource.com/c/1260524Reviewed-by: Alexey Baskakov <loyso@chromium.org>
Commit-Queue: Alexey Baskakov <loyso@chromium.org>
Cr-Commit-Position: refs/heads/master@{#596472}

chrome/browser/autocomplete/search_provider_unittest.cc

@@ -3612,7 +3612,14 @@ TEST_F(SearchProviderTest, DoesNotProvideOnFocus) {
   EXPECT_TRUE(provider_->matches().empty());
 }
 
-TEST_F(SearchProviderTest, SendsWarmUpRequestOnFocus) {
+#if defined(THREAD_SANITIZER)
+// SearchProviderTest.SendsWarmUpRequestOnFocus is flaky on Linux TSan Tests
+// crbug.com/891959.
+#define MAYBE_SendsWarmUpRequestOnFocus DISABLED_SendsWarmUpRequestOnFocus
+#else
+#define MAYBE_SendsWarmUpRequestOnFocus SendsWarmUpRequestOnFocus
+#endif  // defined(THREAD_SANITIZER)
+TEST_F(SearchProviderTest, MAYBE_SendsWarmUpRequestOnFocus) {
   AutocompleteInput input(base::ASCIIToUTF16("f"),
                           metrics::OmniboxEventProto::OTHER,
                           ChromeAutocompleteSchemeClassifier(&profile_));