Implement PasswordStoreProxyMac and SimplePasswordStoreMac.

components/password_manager/core/browser/password_store_default.cc

Index: components/password_manager/core/browser/password_store_default.cc
diff --git a/components/password_manager/core/browser/password_store_default.cc b/components/password_manager/core/browser/password_store_default.cc
index 40b070e32123b50c9d6ac9d4c9c33bc1c07a8cb8..656e54da09b53ece726215d3db9305a8b8f6a8b4 100644
--- a/components/password_manager/core/browser/password_store_default.cc
+++ b/components/password_manager/core/browser/password_store_default.cc
@@ -24,8 +24,6 @@ PasswordStoreDefault::PasswordStoreDefault(
 }
 
 PasswordStoreDefault::~PasswordStoreDefault() {
-  if (!GetBackgroundTaskRunner()->BelongsToCurrentThread())
-    GetBackgroundTaskRunner()->DeleteSoon(FROM_HERE, login_db_.release());
 }
 
 bool PasswordStoreDefault::Init(
@@ -34,6 +32,11 @@ bool PasswordStoreDefault::Init(
   return PasswordStore::Init(flare);
 }
 
+void PasswordStoreDefault::Shutdown() {
+  PasswordStore::Shutdown();
+  GetBackgroundTaskRunner()->DeleteSoon(FROM_HERE, login_db_.release());
+}
+
 void PasswordStoreDefault::InitOnDBThread() {
   DCHECK(GetBackgroundTaskRunner()->BelongsToCurrentThread());
   DCHECK(login_db_);