New CPAT support in ContentLoFiDecider guarded by feature flag.

components/data_reduction_proxy/content/browser/content_lofi_decider.cc

Index: components/data_reduction_proxy/content/browser/content_lofi_decider.cc
diff --git a/components/data_reduction_proxy/content/browser/content_lofi_decider.cc b/components/data_reduction_proxy/content/browser/content_lofi_decider.cc
index 4f98e4eea1b944c2b0e38617618007e909bf3065..2261b4cfd87a050e076035184faf6b76c8b2c028 100644
--- a/components/data_reduction_proxy/content/browser/content_lofi_decider.cc
+++ b/components/data_reduction_proxy/content/browser/content_lofi_decider.cc
@@ -6,9 +6,11 @@
 
 #include <string>
 
+#include "base/feature_list.h"
 #include "base/strings/string_split.h"
 #include "base/strings/string_util.h"
 #include "base/strings/stringprintf.h"
+#include "components/data_reduction_proxy/core/common/data_reduction_proxy_features.h"
 #include "components/data_reduction_proxy/core/common/data_reduction_proxy_headers.h"
 #include "components/data_reduction_proxy/core/common/data_reduction_proxy_params.h"
 #include "content/public/browser/resource_request_info.h"
@@ -67,29 +69,47 @@ void ContentLoFiDecider::MaybeSetAcceptTransformHeader(
     return;
   }
 
-  // The Lo-Fi and Lite Page directives should not be added for users in the
-  // Lo-Fi field trial "Control" group.
-  bool lofi_enabled_via_flags_or_field_trial =
-      params::IsLoFiOnViaFlags() || params::IsIncludedInLoFiEnabledFieldTrial();
-
-  bool lite_page_enabled_via_flags_or_field_trial =
-      (params::IsLoFiOnViaFlags() && params::AreLitePagesEnabledViaFlags()) ||
-      params::IsIncludedInLitePageFieldTrial();
-
-  // User does not have previews enabled.
-  if (!lofi_enabled_via_flags_or_field_trial &&
-      !lite_page_enabled_via_flags_or_field_trial) {
-    return;
-  }
-
-  // Previews has been disabled.
-  if (are_previews_disabled)
-    return;
+  content::PreviewsState previews_state = request_info->GetPreviewsState();
 
   // Do not add the Chrome-Proxy-Accept-Transform header when the page load
   // explicitly forbids previews transformations.
-  if (request_info->GetPreviewsState() & content::PREVIEWS_NO_TRANSFORM)
+  if (previews_state & content::PREVIEWS_NO_TRANSFORM) {
     return;
+  }
+
+  // For the proxy-decides-transform feature, the header is set based only
+  // on the request's PreviewsState (no checking of previews flags).
+  // This is for a newer version of the proxy server protocol where the
+  // server makes the transform decision and client simply advertises
+  // if is accepts transforms for the resource type (determined here from
+  // previously set previews state bits). The previous logic in this method
+  // that checks various flags will be deprecated.
+  bool check_previews_flags = !base::FeatureList::IsEnabled(
+      features::kDataReductionProxyDecidesTransform);
+
+  bool lofi_enabled_via_flags_or_field_trial = false;
+  bool lite_page_enabled_via_flags_or_field_trial = false;
+  if (check_previews_flags) {
+    // The Lo-Fi and Lite Page directives should not be added for users in the
+    // Lo-Fi field trial "Control" group.
+    lofi_enabled_via_flags_or_field_trial =
+        params::IsLoFiOnViaFlags() ||
+        params::IsIncludedInLoFiEnabledFieldTrial();
+
+    lite_page_enabled_via_flags_or_field_trial =
+        (params::IsLoFiOnViaFlags() && params::AreLitePagesEnabledViaFlags()) ||
+        params::IsIncludedInLitePageFieldTrial();
+
+    // Previews have been disabled.
+    if (are_previews_disabled)
+      return;
+
+    // User does not have previews enabled.
+    if (!lofi_enabled_via_flags_or_field_trial &&
+        !lite_page_enabled_via_flags_or_field_trial) {
+      return;
+    }
+  }
 
   // Lo-Fi is not allowed on the main frame, stylesheet, script, font resource,
   // media, service worker, or CSP report.
@@ -101,31 +121,43 @@ void ContentLoFiDecider::MaybeSetAcceptTransformHeader(
         resource_type == content::RESOURCE_TYPE_MEDIA ||
         resource_type == content::RESOURCE_TYPE_CSP_REPORT);
 
-  // If the Lite Page field trial or flag is enabled, only add the "lite-page"
-  // directive on main frame requests. Only add "empty-image" directives to
-  // other requests when Lite Page previews are not enabled after the main
-  // frame. Add the "if-heavy" qualifier to allow the server to provide a
-  // preview when the page is data heavy on if a preview was not otherwise
-  // triggered.
   std::string accept_transform_value;
-  if (lite_page_enabled_via_flags_or_field_trial &&
-      resource_type == content::RESOURCE_TYPE_MAIN_FRAME) {
+  if (!check_previews_flags) {
+    // For the proxy-decides-transform feature, check PreviewsState bits and
+    // type of resource to determine which, if any, transformation to accept.
+    if ((previews_state & content::SERVER_LITE_PAGE_ON) &&
+        resource_type == content::RESOURCE_TYPE_MAIN_FRAME) {
+      accept_transform_value = lite_page_directive();
+    } else if ((previews_state & content::SERVER_LOFI_ON) &&
+               resource_type_supports_empty_image) {
+      // Note that for subresource requests, the Lo-Fi bit should only be set
+      // if the main frame response provided the "empty-image" directive (for
+      // the client to echo back to the server here for any image resources).
+      accept_transform_value = empty_image_directive();
+    }
+  } else if (lite_page_enabled_via_flags_or_field_trial &&
+             resource_type == content::RESOURCE_TYPE_MAIN_FRAME) {
+    // If the Lite Page field trial or flag is enabled, only add the "lite-page"
+    // directive on main frame requests. Only add "empty-image" directives to
+    // other requests when Lite Page previews are not enabled after the main
+    // frame. Add the "if-heavy" qualifier to allow the server to provide a
+    // preview when the page is data heavy on if a preview was not otherwise
+    // triggered.
     accept_transform_value = lite_page_directive();
 
     // Since a Lite Page was not triggered client side, ask the server to
     // provide a Lite Page only if the page is otherwise data-heavy.
-    if (!(request_info->GetPreviewsState() & content::SERVER_LITE_PAGE_ON))
+    if (!(previews_state & content::SERVER_LITE_PAGE_ON))
       accept_transform_value += base::StringPrintf(";%s", if_heavy_qualifier());
   } else if (lofi_enabled_via_flags_or_field_trial &&
              !lite_page_enabled_via_flags_or_field_trial &&
              resource_type_supports_empty_image &&
-             !(request_info->GetPreviewsState() &
-               content::SERVER_LITE_PAGE_ON)) {
+             !(previews_state & content::SERVER_LITE_PAGE_ON)) {
     accept_transform_value = empty_image_directive();
 
     // Since Lo-Fi was not triggered client side, ask the server to provide
     // Lo-Fi only if the page is otherwise data-heavy.
-    if (!(request_info->GetPreviewsState() & content::SERVER_LOFI_ON))
+    if (!(previews_state & content::SERVER_LOFI_ON))
       accept_transform_value += base::StringPrintf(";%s", if_heavy_qualifier());
   }
   if (accept_transform_value.empty())