Add brotli content-encoding filter.

net/BUILD.gn

Index: net/BUILD.gn
diff --git a/net/BUILD.gn b/net/BUILD.gn
index 4ca6128f1888119f336ed9d40fcce6e5236103d3..df31b0deade654747e25092d96516f3ddbb8a4dc 100644
--- a/net/BUILD.gn
+++ b/net/BUILD.gn
@@ -451,11 +451,16 @@ component("net") {
       "base/net_string_util_icu.cc",
       "base/net_util_icu.cc",
     ]
+
+    # Brotli support.
+    deps += [ "//third_party/brotli" ]
+    sources += [ "filter/brotli_filter.cc" ]
   }
 }
 
 if (is_android) {
-  # Same as net, but with ICU, file, ftp, and websocket support stripped.
+  # Same as net, but with brotli encoding, ICU, file, ftp, and websocket
+  # support stripped.
   component("net_small") {
     sources = net_shared_sources
 
@@ -484,6 +489,9 @@ 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" ]
   }
 }