Add brotli content-encoding filter.

net/BUILD.gn

Index: net/BUILD.gn
diff --git a/net/BUILD.gn b/net/BUILD.gn
index 4ca6128f1888119f336ed9d40fcce6e5236103d3..81b5323bccb1f699779b698d21941610094fa686 100644
--- a/net/BUILD.gn
+++ b/net/BUILD.gn
@@ -451,6 +451,10 @@ component("net") {
       "base/net_string_util_icu.cc",
       "base/net_util_icu.cc",
     ]
+
+    # Brotli support.
+    deps += [ "//third_party/brotli" ]
+    sources += [ "filter/brotli_filter.cc" ]
   }
 }
 
@@ -484,6 +488,9 @@ if (is_android) {
       "base/net_string_util_icu_alternatives_android.cc",
       "base/net_string_util_icu_alternatives_android.h",
     ]
+
+    # Disable Brotli support.
+    sources += [ "filter/brotli_filter_disabled.cc" ]
   }
 }