Implement InstanceID API functions.

chrome/browser/services/gcm/instance_id/instance_id_profile_service.cc

Index: chrome/browser/services/gcm/instance_id/instance_id_profile_service.cc
diff --git a/chrome/browser/services/gcm/instance_id/instance_id_profile_service.cc b/chrome/browser/services/gcm/instance_id/instance_id_profile_service.cc
index 60d3c2a04a24400a7bfd9d7c5cb96629dd404cf0..47a6f3a06ca398a748512b1369e86e658217662e 100644
--- a/chrome/browser/services/gcm/instance_id/instance_id_profile_service.cc
+++ b/chrome/browser/services/gcm/instance_id/instance_id_profile_service.cc
@@ -8,10 +8,25 @@
 #include "chrome/browser/profiles/profile.h"
 #include "chrome/browser/services/gcm/gcm_profile_service.h"
 #include "chrome/browser/services/gcm/gcm_profile_service_factory.h"
+#include "chrome/common/chrome_version_info.h"
 #include "components/gcm_driver/instance_id/instance_id_driver.h"
 
 namespace instance_id {
 
+// static
+bool InstanceIDProfileService::IsInstanceIDEnabled(Profile* profile) {
+  // Instance ID depends on GCM which has to been enabled.
+  if (!gcm::GCMProfileService::IsGCMEnabled(profile))
+    return false;
+
+  // Enabled for trunk build.
+  chrome::VersionInfo::Channel channel = chrome::VersionInfo::GetChannel();
+  if (channel == chrome::VersionInfo::CHANNEL_UNKNOWN)
+    return true;
+
+  return InstanceIDDriver::IsInstanceIDEnabled();
+}
+
 InstanceIDProfileService::InstanceIDProfileService(Profile* profile) {
   DCHECK(!profile->IsOffTheRecord());