Move --user-agent overriding logic from chrome into content.

content/public/common/content_client.h

Index: content/public/common/content_client.h
diff --git a/content/public/common/content_client.h b/content/public/common/content_client.h
index 4e6612d0dd57a1da868fe932ca2f90a68a599a0f..d487db06dff918a5551d9cd4aa0ea04dd00000ee 100644
--- a/content/public/common/content_client.h
+++ b/content/public/common/content_client.h
@@ -98,10 +98,8 @@ class CONTENT_EXPORT ContentClient {
   // behalf of a swapped out renderer.
   virtual bool CanHandleWhileSwappedOut(const IPC::Message& msg) = 0;
 
-  // Returns the user agent and a flag indicating whether the returned
-  // string should always be used (if false, callers may override the
-  // value as needed to work around various user agent sniffing bugs).
-  virtual std::string GetUserAgent(bool *overriding) const = 0;
+  // Returns the user agent.
+  virtual std::string GetUserAgent() const = 0;
 
   // Returns a string resource given its id.
   virtual string16 GetLocalizedString(int message_id) const = 0;