Fix a flakiness in the TabLifeCycleUnit tests

The bug causing
TabLifecycleUnitTest.CannotFreezeOrDiscardIfConnectedToBluetooth was due to
the test running right before it, which was modifying a global state
without resetting it to the proper value.

Bug: 1004578
Change-Id: I0c8fa306e0d2f40911c18de52c062352d380fb5f
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1808335
Commit-Queue: Sébastien Marchand <sebmarchand@chromium.org>
Auto-Submit: Sébastien Marchand <sebmarchand@chromium.org>
Reviewed-by: François Doray <fdoray@chromium.org>
Cr-Commit-Position: refs/heads/master@{#697699}

chrome/browser/resource_coordinator/tab_lifecycle_unit_unittest.cc

@@ -7,6 +7,7 @@
 #include <memory>
 #include <string>
 
+#include "base/auto_reset.h"
 #include "base/bind.h"
 #include "base/macros.h"
 #include "base/observer_list.h"
@@ -888,8 +889,10 @@ TEST_F(TabLifecycleUnitTest, DisableHeuristicsFlag) {
   decision_details.Clear();
 
   // Disable the heuristics and check that the tab can now be safely discarded.
-  GetMutableStaticProactiveTabFreezeAndDiscardParamsForTesting()
-      ->disable_heuristics_protections = true;
+  base::AutoReset<bool> disable_heuristics_protections(
+      &GetMutableStaticProactiveTabFreezeAndDiscardParamsForTesting()
+           ->disable_heuristics_protections,
+      true);
 
   EXPECT_TRUE(tab_lifecycle_unit.CanFreeze(&decision_details));
   EXPECT_TRUE(decision_details.IsPositive());
@@ -901,9 +904,7 @@ TEST_F(TabLifecycleUnitTest, DisableHeuristicsFlag) {
   decision_details.Clear();
 }
 
-// TODO(crbug.com/1004578) Disabled due to flake
-TEST_F(TabLifecycleUnitTest,
-       DISABLED_CannotFreezeOrDiscardIfConnectedToBluetooth) {
+TEST_F(TabLifecycleUnitTest, CannotFreezeOrDiscardIfConnectedToBluetooth) {
   TabLifecycleUnit tab_lifecycle_unit(GetTabLifecycleUnitSource(), &observers_,
                                       usage_clock_.get(), web_contents_,
                                       tab_strip_model_.get());