Added support for heavy page previews transformations

components/data_reduction_proxy/core/common/data_reduction_proxy_headers.h

Index: components/data_reduction_proxy/core/common/data_reduction_proxy_headers.h
diff --git a/components/data_reduction_proxy/core/common/data_reduction_proxy_headers.h b/components/data_reduction_proxy/core/common/data_reduction_proxy_headers.h
index b0ea201384ef6f926c3137ebf57335ae616b3c6b..8074f9d59813a8300c96d8fc250c41fdb9577a61 100644
--- a/components/data_reduction_proxy/core/common/data_reduction_proxy_headers.h
+++ b/components/data_reduction_proxy/core/common/data_reduction_proxy_headers.h
@@ -101,6 +101,11 @@ const char* chrome_proxy_lite_page_directive();
 // preview experiment to ignore the blacklist.
 const char* chrome_proxy_lite_page_ignore_blacklist_directive();
 
+// Requests a transformation only if the server determines that the page is

[RyanSturm, 2016/10/19 18:58:57]

nit:s/page/resource/  ?

[bengr, 2016/10/19 23:34:28]

Nope, the server looks at the enclosing page. Easy for lite pages, harder for
LoFi.

[RyanSturm, 2016/10/19 23:43:12]

Weird. sgtm.

+// otherwise heavy (requires the network transfer of a lot of bytes). Added

[RyanSturm, 2016/10/19 18:58:56]

nit: s/(requires the network transfer/ (i.e., the resource ordinarily requires
the network to transfer/

[bengr, 2016/10/19 23:34:28]

Done.

+// to a previews directive. E.g., "lite-page;if-heavy".
+const char* if_heavy_qualifier();
+
 // Returns true if the Chrome-Proxy-Content-Transform response header indicates
 // that an empty image has been provided.
 bool IsEmptyImagePreview(const net::HttpResponseHeaders& headers);