Add brotli content-encoding filter.

net/BUILD.gn

Index: net/BUILD.gn
diff --git a/net/BUILD.gn b/net/BUILD.gn
index 7403fe2a68de1550f33ec7d126d2a2d62af58d8b..401bcf424896d786043a6256422ee5528b807475 100644
--- a/net/BUILD.gn
+++ b/net/BUILD.gn
@@ -41,6 +41,7 @@ posix_avoid_mmap = is_android && current_cpu != "x86"
 enable_websockets = !is_ios
 use_v8_in_net = !is_ios
 enable_built_in_dns = !is_ios
+disable_brotli_support = is_ios
 disable_ftp_support = is_ios
 
 declare_args() {
@@ -121,6 +122,10 @@ if (!is_nacl) {
     "//third_party/zlib",
   ]
 
+  if (!disable_brotli_support) {
+    net_shared_deps += [ "//third_party/brotli" ]
+  }
+
   if (!use_kerberos) {
     net_shared_sources -= [
       "http/http_auth_gssapi_posix.cc",
@@ -1372,6 +1377,7 @@ test("net_unittests") {
     "//sql",
     "//testing/gmock",
     "//testing/gtest",
+    "//third_party/brotli",
     "//third_party/zlib",
     "//url",
   ]
@@ -1524,6 +1530,11 @@ test("net_unittests") {
     ]
   }
 
+  if (disable_brotli_support) {
+    sources -= [ "filter/brotli_filter_unittest.cc" ]
+    deps -= [ "//third_party/brotli" ]
+  }
+
   if (!enable_built_in_dns) {
     sources -= [
       "dns/address_sorter_posix_unittest.cc",