Refactor SetOmahaExperimentLabel out of gcpai and into install_util.

chrome/installer/gcapi/gcapi_omaha_experiment.h

Index: chrome/installer/gcapi/gcapi_omaha_experiment.h
diff --git a/chrome/installer/gcapi/gcapi_omaha_experiment.h b/chrome/installer/gcapi/gcapi_omaha_experiment.h
index 16fbdb35777209148228796cb96ebda056f256fd..a59a6264f2e5517a60152925bf3ffbf9893e5c6a 100644
--- a/chrome/installer/gcapi/gcapi_omaha_experiment.h
+++ b/chrome/installer/gcapi/gcapi_omaha_experiment.h
@@ -5,6 +5,11 @@
 #ifndef CHROME_INSTALLER_GCAPI_GCAPI_OMAHA_EXPERIMENT_H_
 #define CHROME_INSTALLER_GCAPI_GCAPI_OMAHA_EXPERIMENT_H_
 
-bool SetOmahaExperimentLabel(const wchar_t* brand_code, int shell_mode);
+// Writes a reactivation brand code experiment label in the Chrome product and
+// binaries registry keys for |brand_code|. This experiment label will have a
+// expiration date of now plus one year. If |shell_mode| is set to
+// GCAPI_INVOKED_UAC_ELEVATION, the value will be written to HKLM, otherwise
+// HKCU.
+bool SetGCAPIOmahaExperimentLabel(const wchar_t* brand_code, int shell_mode);
 
 #endif  // CHROME_INSTALLER_GCAPI_GCAPI_OMAHA_EXPERIMENT_H_