Set magic string in registry to enable fallback to full installer in case of 3 stage updates.

chrome/installer/mini_installer/mini_installer.h

Index: chrome/installer/mini_installer/mini_installer.h
diff --git a/chrome/installer/mini_installer/mini_installer.h b/chrome/installer/mini_installer/mini_installer.h
index b1afc193515f15bd475230792cee17072f9b4547..fde36566fbe1e247d7ecdac2e688efa3706b9ed3 100644
--- a/chrome/installer/mini_installer/mini_installer.h
+++ b/chrome/installer/mini_installer/mini_installer.h
@@ -24,6 +24,8 @@ const wchar_t kCmdNewSetupExe[] = L" --new-setup-exe";
 
 // Temp directory prefix that this process creates
 const wchar_t kTempPrefix[] = L"CR_";
+// Google Update will use full installer if this suffix is found in ap key.
+const wchar_t kFullInstallerSuffix[] = L"-full";
 
 // The resource types that would be unpacked from the mini installer.
 // 'BN' is uncompressed binary and 'BL' is LZ compressed binary.
@@ -32,15 +34,21 @@ const wchar_t kLZCResourceType[] = L"BL";
 const wchar_t kLZMAResourceType[] = L"B7";
 
 // Registry key to get uninstall command
-const wchar_t kUninstallRegistryValueName[] = L"UninstallString";
+const wchar_t kApRegistryValueName[] = L"ap";
 // Registry key that tells Chrome installer not to delete extracted files.
 const wchar_t kCleanupRegistryValueName[] = L"ChromeInstallerCleanup";
-// Paths for the above two registry keys
+// Registry key to get uninstall command
+const wchar_t kUninstallRegistryValueName[] = L"UninstallString";
+
+// Paths for the above registry keys
 #if defined(GOOGLE_CHROME_BUILD)
+const wchar_t kApRegistryKey[] = L"Software\\Google\\Update\\ClientState\\"
+                                 L"{8A69D345-D564-463c-AFF1-A69D9E530F96}";
 const wchar_t kUninstallRegistryKey[] =
     L"Software\\Microsoft\\Windows\\CurrentVersion\\Uninstall\\Google Chrome";
 const wchar_t kCleanupRegistryKey[] = L"Software\\Google";
 #else
+const wchar_t kApRegistryKey[] = L"Software\\Chromium";
 const wchar_t kUninstallRegistryKey[] =
     L"Software\\Microsoft\\Windows\\CurrentVersion\\Uninstall\\Chromium";
 const wchar_t kCleanupRegistryKey[] = L"Software\\Chromium";