Adds Server Previews protocol UMA plus UMA for not accepting previews

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 2415143b978de1edd9351cf5baaad0f3d189b844..1a79dfb7129cf61bcaabcf83c890d355a0971671 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
@@ -11,6 +11,8 @@
 #include "base/macros.h"
 #include "base/strings/string_piece.h"
 #include "base/time/time.h"
+#include "net/http/http_request_headers.h"
+#include "net/http/http_response_headers.h"
 #include "net/proxy/proxy_service.h"
 
 class GURL;
@@ -21,6 +23,15 @@ class HttpResponseHeaders;
 
 namespace data_reduction_proxy {
 
+// Transform types that may be parsed out of http headers.

[bengr, 2017/06/28 16:45:51]

http -> http response

[dougarnett, 2017/06/28 22:12:39]

but also request headers (was trying to avoid defining twice)

+enum TransformType {

[bengr, 2017/06/28 16:45:51]

A policy isn't a transform type. How about "TransformAnnotations" ?

[dougarnett, 2017/06/28 22:12:39]

DIRECTIVE? That terminoloy is used on the constant names.

[bengr, 2017/06/29 00:25:05]

Sgtm.

+  TRANSFORM_NONE,

[bengr, 2017/06/28 16:45:51]

Do we need the prefix "TRANSFORM_" ?

[dougarnett, 2017/06/28 22:12:39]

Wanted to avoid confusion with PreviewsState::LITE_PAGE et al.
These are about the proxy proto which uses the transform terminology
(CPAT/CPCT).
Was thinking of keeping narrow scope on this enum for now as we indeed may want
to instead parse into a struct instead if it gets more complicated (eg, both
CPCT and page-policies or multiple page-policies values).

+  TRANSFORM_LITE_PAGE,
+  TRANSFORM_EMPTY_IMAGE,
+  TRANSFORM_COMPRESS_VIDEO,

[bengr, 2017/06/28 16:45:51]

Is this a request or a response? If the latter (and maybe also the former),
"COMPRESSED" might make more sense. 

[dougarnett, 2017/06/28 22:12:38]

Done.

+  TRANSFORM_PAGE_POLICIES_EMPTY_IMAGE,
+};
+
 // Values of the UMA DataReductionProxy.BypassType{Primary|Fallback} and
 // DataReductionProxy.BlockType{Primary|Fallback} histograms. This enum must
 // remain synchronized with the enum of the same name in
@@ -116,6 +127,12 @@ const char* if_heavy_qualifier();
 // that an empty image has been provided.
 bool IsEmptyImagePreview(const net::HttpResponseHeaders& headers);
 
+// Parse out the type of accepted transform, if any, in |headers|.

[bengr, 2017/06/28 16:45:51]

How about:
// Retrieve the transform type, if any, from |headers|.


Also, it's worth saying that |headers| must contain at most one transform type,
and that you will do something specific if more than
one appears in headers.

[dougarnett, 2017/06/28 22:12:38]

Done - added note about behavior for dual transforms to next method (that
handles responses).

+TransformType ParseRequestTransform(const net::HttpRequestHeaders& headers);
+
+// Parse out the type of content transform, if any, in |headers|.
+TransformType ParseResponseTransform(const net::HttpResponseHeaders& headers);
+
 // Returns true if the provided value of the Chrome-Proxy-Content-Transform
 // response header that is provided in |content_transform_value| indicates that
 // an empty image has been provided.