Add a new GetInstance() method for singleton classes used in chrome/browser files.

chrome/browser/zygote_host_linux.h

Index: chrome/browser/zygote_host_linux.h
diff --git a/chrome/browser/zygote_host_linux.h b/chrome/browser/zygote_host_linux.h
index ffb7964b032ad813f509fdb1bf961e0c7b9e42ec..01a64435cf86ead1be5800da5d838ec80b75b693 100644
--- a/chrome/browser/zygote_host_linux.h
+++ b/chrome/browser/zygote_host_linux.h
@@ -26,6 +26,9 @@ static const char kZygoteMagic[] = "ZYGOTE_OK";
 // process.
 class ZygoteHost {
  public:
+  // Returns the singleton instance.
+  static ZygoteHost* GetInstance();
+
   void Init(const std::string& sandbox_cmd);
 
   // Tries to start a renderer process.  Returns its pid on success, otherwise