Enable QUIC for proxies based on Finch config and command line switch.

chrome/browser/io_thread.h

Index: chrome/browser/io_thread.h
diff --git a/chrome/browser/io_thread.h b/chrome/browser/io_thread.h
index 3fbbe9ea0475a77def068621e0572f89d21a0c48..0073ff676f26983e29789298d4fb6f0d9a7bd63e 100644
--- a/chrome/browser/io_thread.h
+++ b/chrome/browser/io_thread.h
@@ -182,6 +182,7 @@ class IOThread : public content::BrowserThreadDelegate {
     Optional<double> alternate_protocol_probability_threshold;
 
     Optional<bool> enable_quic;
+    Optional<bool> enable_quic_for_proxies;
     Optional<bool> enable_quic_port_selection;
     Optional<bool> quic_always_require_handshake_confirmation;
     Optional<bool> quic_disable_connection_pooling;
@@ -236,6 +237,10 @@ class IOThread : public content::BrowserThreadDelegate {
 
   base::TimeTicks creation_time() const;
 
+  // Returns true if QUIC should be enabled for proxies, either as a result
+  // of a field trial or a command line flag.
+  static bool ShouldEnableQuicForProxies();
+
  private:
   // Map from name to value for all parameters associate with a field trial.
   typedef std::map<std::string, std::string> VariationParameters;