Fix google-explicit-constructor warnings.

Bug: 28341362
Change-Id: I4504e98a8db31e0edcbe63c23f9af43eb13e9d86
diff --git a/init/action.cpp b/init/action.cpp
index 510ea89..b7e431c 100644
--- a/init/action.cpp
+++ b/init/action.cpp
@@ -264,7 +264,7 @@
 
 class EventTrigger : public Trigger {
 public:
-    EventTrigger(const std::string& trigger) : trigger_(trigger) {
+    explicit EventTrigger(const std::string& trigger) : trigger_(trigger) {
     }
     bool CheckTriggers(const Action& action) const override {
         return action.CheckEventTrigger(trigger_);
@@ -288,7 +288,7 @@
 
 class BuiltinTrigger : public Trigger {
 public:
-    BuiltinTrigger(Action* action) : action_(action) {
+    explicit BuiltinTrigger(Action* action) : action_(action) {
     }
     bool CheckTriggers(const Action& action) const override {
         return action_ == &action;