Make setting the user agent work with the zygote on linux.

webkit/glue/webkit_glue.cc

Index: webkit/glue/webkit_glue.cc
diff --git a/webkit/glue/webkit_glue.cc b/webkit/glue/webkit_glue.cc
index 1d8930577160eccdc754a36141b5232720b21494..25c991322dbc3ccc3cadc6464fda55cd30c1a342 100644
--- a/webkit/glue/webkit_glue.cc
+++ b/webkit/glue/webkit_glue.cc
@@ -344,6 +344,7 @@ class UserAgentState {
   ~UserAgentState();
 
   void Set(const std::string& user_agent, bool overriding);
+  void Reset(const std::string& user_agent, bool overriding);
   const std::string& Get(const GURL& url) const;
 
  private:
@@ -375,9 +376,16 @@ void UserAgentState::Set(const std::string& user_agent, bool overriding) {
     // given g_user_agent is a global.
     return;
   }
-  DCHECK(!user_agent.empty());
   DCHECK(!user_agent_requested_) << "Setting the user agent after someone has "
       "already requested it can result in unexpected behavior.";
+  lock_.Release();
+  UserAgentState::Reset(user_agent, overriding);
+  lock_.Acquire();
+}
+
+void UserAgentState::Reset(const std::string& user_agent, bool overriding) {
+  base::AutoLock auto_lock(lock_);
+  DCHECK(!user_agent.empty());
   user_agent_is_overridden_ = overriding;
   user_agent_ = user_agent;
 }
@@ -417,6 +425,10 @@ void SetUserAgent(const std::string& user_agent, bool overriding) {
   g_user_agent.Get().Set(user_agent, overriding);
 }
 
+void ResetUserAgent(const std::string& user_agent, bool overriding) {
+  g_user_agent.Get().Reset(user_agent, overriding);
+}
+
 const std::string& GetUserAgent(const GURL& url) {
   return g_user_agent.Get().Get(url);
 }