Refactor SetOmahaExperimentLabel out of gcpai and into install_util.

chrome/installer/util/google_update_constants.h

Index: chrome/installer/util/google_update_constants.h
diff --git a/chrome/installer/util/google_update_constants.h b/chrome/installer/util/google_update_constants.h
index 8c1aceed4dd6adb079fcc295bb6f4dd1bc283779..54c8e7b7b4f110f7d87fa3b8533466206a29a140 100644
--- a/chrome/installer/util/google_update_constants.h
+++ b/chrome/installer/util/google_update_constants.h
@@ -11,6 +11,11 @@ namespace google_update {
 
 // The GUID Google Update uses to keep track of Chrome upgrades.
 extern const wchar_t kChromeUpgradeCode[];
+
+// The name of the value where Google Update reads the list of experiments for
+// itself and Chrome.
+extern const wchar_t kExperimentLabels[];
+
 // The GUID Google Update uses to keep track of Google Update self-upgrades.
 extern const wchar_t kGoogleUpdateUpgradeCode[];