Revert "Remove webkit_glue::BuildUserAgent(), change the contract in webkit_glue"

webkit/glue/webkit_glue.h

Index: webkit/glue/webkit_glue.h
diff --git a/webkit/glue/webkit_glue.h b/webkit/glue/webkit_glue.h
index 37a56a466e1d86fb49d16883860bb237a0d1039b..54cfdc1f29aaa9099f33b0dddb42cb704e4c88a4 100644
--- a/webkit/glue/webkit_glue.h
+++ b/webkit/glue/webkit_glue.h
@@ -88,14 +88,14 @@ string16 DumpFrameScrollPosition(WebKit::WebFrame* web_frame, bool recursive);
 string16 DumpHistoryState(const std::string& history_state, int indent,
                           bool is_current);
 
-// Sets the user agent.  Pass true for overriding if this is a custom
-// user agent instead of the default one (in order to turn off any browser
-// sniffing workarounds). This must be called before GetUserAgent() can
-// be called.
-void SetUserAgent(const std::string& user_agent, bool overriding);
-
-// Returns the user agent to use for the given URL. SetUserAgent() must
-// be called prior to calling this function.
+// Called to override the default user agent with a custom one.  Call this
+// before anyone actually asks for the user agent in order to prevent
+// inconsistent behavior.
+void SetUserAgent(const std::string& new_user_agent);
+
+// Returns the user agent to use for the given URL, which is usually the
+// default user agent but may be overriden by a call to SetUserAgent() (which
+// should be done at startup).
 const std::string& GetUserAgent(const GURL& url);
 
 // Creates serialized state for the specified URL. This is a variant of
@@ -147,6 +147,10 @@ WebKit::WebCanvas* ToWebCanvas(skia::PlatformCanvas*);
 // used to get memory usage statistics.
 int GetGlyphPageCount();
 
+// Construct the User-Agent header, filling in |result|.
+// - If mimic_windows is true, produce a fake Windows Chrome string.
+std::string BuildUserAgent(bool mimic_windows);
+
 //---- END FUNCTIONS IMPLEMENTED BY WEBKIT/GLUE -------------------------------