Add brotli content-encoding filter.

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 f156ebd5b0247f646e28ea1b2c7e04476f27cddd..f2505eadfeafdf3225dabf0913babff2635fcb48 100644
--- a/chrome/browser/io_thread.h
+++ b/chrome/browser/io_thread.h
@@ -210,6 +210,8 @@ class IOThread : public content::BrowserThreadDelegate {
 
     Optional<bool> enable_npn;
 
+    Optional<bool> enable_brotli;
+
     Optional<bool> enable_quic;
     Optional<bool> enable_quic_for_proxies;
     Optional<bool> enable_quic_port_selection;
@@ -346,6 +348,10 @@ class IOThread : public content::BrowserThreadDelegate {
     return NULL;
 #endif
   }
+
+  // Returns true if Brotli Content-Encoding should be enabled.
+  static bool ShouldEnableBrotli(const base::CommandLine& command_line);
+
   // Configures QUIC options in |globals| based on the flags in |command_line|
   // as well as the QUIC field trial group and parameters.  Must be called
   // before ConfigureSpdyGlobals.