chromeos: Explicitly initialize and shut down UpgradeDetectorChromeos.

chrome/browser/chromeos/upgrade_detector_chromeos.cc

Index: chrome/browser/chromeos/upgrade_detector_chromeos.cc
diff --git a/chrome/browser/chromeos/upgrade_detector_chromeos.cc b/chrome/browser/chromeos/upgrade_detector_chromeos.cc
index e8fe6c5df78ba0a4875829c7fdd39b3c18e37a52..653c4bb5a3b2ffe0a054d68cbdfc65b376ace4e3 100644
--- a/chrome/browser/chromeos/upgrade_detector_chromeos.cc
+++ b/chrome/browser/chromeos/upgrade_detector_chromeos.cc
@@ -15,12 +15,22 @@ const int kNotifyCycleTimeMs = 20 * 60 * 1000;  // 20 minutes.
 
 }  // namespace
 
-UpgradeDetectorChromeos::UpgradeDetectorChromeos() {
+UpgradeDetectorChromeos::UpgradeDetectorChromeos() : initialized_(false) {
+}
+
+UpgradeDetectorChromeos::~UpgradeDetectorChromeos() {
+}
+
+void UpgradeDetectorChromeos::Init() {
   if (chromeos::CrosLibrary::Get())
     chromeos::CrosLibrary::Get()->GetUpdateLibrary()->AddObserver(this);
+  initialized_ = true;
 }
 
-UpgradeDetectorChromeos::~UpgradeDetectorChromeos() {
+void UpgradeDetectorChromeos::Shutdown() {
+  // Init() may not be called from tests (ex. BrowserMainTest).
+  if (!initialized_)
+    return;
   if (chromeos::CrosLibrary::Get())
     chromeos::CrosLibrary::Get()->GetUpdateLibrary()->RemoveObserver(this);
 }