ExtensionFunction: don't pass ownership of base::Value by raw pointer.

extensions/browser/api/idle/idle_manager.cc

Index: extensions/browser/api/idle/idle_manager.cc
diff --git a/extensions/browser/api/idle/idle_manager.cc b/extensions/browser/api/idle/idle_manager.cc
index cecb1e23f8e03e3fc1d74e49792669602b4f173c..7122b6baa783f808916fc334f4af4f070cc3d986 100644
--- a/extensions/browser/api/idle/idle_manager.cc
+++ b/extensions/browser/api/idle/idle_manager.cc
@@ -6,6 +6,7 @@
 
 #include <utility>
 
+#include "base/memory/ptr_util.h"
 #include "base/stl_util.h"
 #include "content/public/browser/browser_context.h"
 #include "extensions/browser/api/idle/idle_api_constants.h"
@@ -180,7 +181,8 @@ void IdleManager::SetThreshold(const std::string& extension_id, int threshold) {
 }
 
 // static
-base::StringValue* IdleManager::CreateIdleValue(ui::IdleState idle_state) {
+std::unique_ptr<base::StringValue> IdleManager::CreateIdleValue(
+    ui::IdleState idle_state) {
   const char* description;
 
   if (idle_state == ui::IDLE_STATE_ACTIVE) {
@@ -191,7 +193,7 @@ base::StringValue* IdleManager::CreateIdleValue(ui::IdleState idle_state) {
     description = keys::kStateLocked;
   }
 
-  return new base::StringValue(description);
+  return base::MakeUnique<base::StringValue>(description);
 }
 
 void IdleManager::SetEventDelegateForTest(