Isolate tests by running AtExit callbacks between them.

base/lazy_instance.cc

Index: base/lazy_instance.cc
diff --git a/base/lazy_instance.cc b/base/lazy_instance.cc
index 388622ae83ebf6a11c0a757f1e57c8a6c87c2aef..992325339cfcbabf3babf92dee3488cd55c2f862 100644
--- a/base/lazy_instance.cc
+++ b/base/lazy_instance.cc
@@ -27,7 +27,14 @@ void LazyInstanceHelper::EnsureInstance(void* instance,
 
     // Instance is created, go from CREATING to CREATED.
     base::subtle::Release_Store(&state_, STATE_CREATED);
-    // Register the destructor callback with AtExitManager.
+
+    // Allow reusing the LazyInstance (reset it to the initial state). This
+    // makes possible calling all AtExit callbacks between tests. Assumes that
+    // no other threads execute when AtExit callbacks are processed.
+    base::AtExitManager::RegisterCallback(&LazyInstanceHelper::ResetState,
+                                          this);
+
+    // Make sure that the lazily instantiated object will get destroyed at exit.
     base::AtExitManager::RegisterCallback(dtor, instance);
   } else {
     // It's either in the process of being created, or already created.  Spin.
@@ -36,4 +43,9 @@ void LazyInstanceHelper::EnsureInstance(void* instance,
   }
 }
 
+// static
+void LazyInstanceHelper::ResetState(void* helper) {
+  reinterpret_cast<LazyInstanceHelper*>(helper)->state_ = STATE_EMPTY;
+}
+
 }  // namespace base