Add brotli content-encoding filter.

net/filter/filter.h

Index: net/filter/filter.h
diff --git a/net/filter/filter.h b/net/filter/filter.h
index 1904a8cdbb957be08b6baf3ef509d56a130a31ec..0b00e6c5468efb4e2b39cb69610183159ea37fab 100644
--- a/net/filter/filter.h
+++ b/net/filter/filter.h
@@ -151,6 +151,7 @@ class NET_EXPORT_PRIVATE Filter {
 
   // Specifies type of filters that can be created.
   enum FilterType {
+    FILTER_TYPE_BROTLI,
     FILTER_TYPE_DEFLATE,
     FILTER_TYPE_GZIP,
     FILTER_TYPE_GZIP_HELPING_SDCH,  // Gzip possible, but pass through allowed.
@@ -231,6 +232,8 @@ class NET_EXPORT_PRIVATE Filter {
   std::string OrderedFilterList() const;
 
  protected:
+  friend class BrotliFilter;

[Ryan Sleevi, 2015/12/17 01:04:40]

^ this strikes me as an anti-pattern, as it represents circular layering. Could
you explain more?

[eustas, 2015/12/17 16:44:54]

For some reason InitBuffer is a private method. I've baked its invocation into
CreateBrotliFilter to have the least amount of added code to filter.cc
Rolled back.

+  friend class BrotliUnitTest;
   friend class GZipUnitTest;
   friend class SdchFilterChainingTest;
   FRIEND_TEST_ALL_PREFIXES(FilterTest, ThreeFilterChain);