HTTPS Previews: Use the DRP experiment instead of a Finch-provided one

This experiment doesn't actually seem very useful in Finch. It's better
to reuse the DRP experiment which is accessible in chrome://flags.

Bug: 934376
Change-Id: I27a5bdfa4f57fa761eaae62106113e7fc5529ba1
Reviewed-on: https://chromium-review.googlesource.com/c/1481995Reviewed-by: Ryan Sturm <ryansturm@chromium.org>
Commit-Queue: Robert Ogden <robertogden@chromium.org>
Cr-Commit-Position: refs/heads/master@{#634682}

chrome/browser/previews/previews_lite_page_navigation_throttle.cc

@@ -11,6 +11,7 @@
 
 #include "base/bind.h"
 #include "base/callback.h"
+#include "base/command_line.h"
 #include "base/memory/weak_ptr.h"
 #include "base/metrics/histogram_macros.h"
 #include "base/optional.h"
@@ -36,6 +37,7 @@
 #include "components/content_settings/core/common/cookie_settings_base.h"
 #include "components/data_reduction_proxy/core/browser/data_reduction_proxy_request_options.h"
 #include "components/data_reduction_proxy/core/common/data_reduction_proxy_headers.h"
+#include "components/data_reduction_proxy/core/common/data_reduction_proxy_switches.h"
 #include "components/previews/core/previews_experiments.h"
 #include "components/previews/core/previews_lite_page_redirect.h"
 #include "content/public/browser/browser_context.h"
@@ -319,7 +321,8 @@ GURL PreviewsLitePageNavigationThrottle::GetPreviewsURLForURL(
     const GURL& original_url) {
   DCHECK(original_url.is_valid());
   std::string experiment_id =
-      previews::params::LitePageRedirectPreviewExperiment();
+      base::CommandLine::ForCurrentProcess()->GetSwitchValueASCII(
+          data_reduction_proxy::switches::kDataReductionProxyExperiment);
   std::string experiment_query;
   if (!experiment_id.empty()) {
     experiment_query =

chrome/browser/previews/previews_lite_page_navigation_throttle_unittest.cc

@@ -6,6 +6,7 @@
 
 #include <memory>
 
+#include "base/command_line.h"
 #include "base/memory/ptr_util.h"
 #include "base/metrics/field_trial.h"
 #include "base/metrics/field_trial_params.h"
@@ -13,6 +14,7 @@
 #include "base/test/scoped_task_environment.h"
 #include "chrome/browser/previews/previews_lite_page_decider.h"
 #include "chrome/test/base/chrome_render_view_host_test_harness.h"
+#include "components/data_reduction_proxy/core/common/data_reduction_proxy_switches.h"
 #include "components/previews/core/previews_features.h"
 #include "content/public/browser/navigation_handle.h"
 #include "net/http/http_util.h"
@@ -97,11 +99,14 @@ TEST(PreviewsLitePageNavigationThrottleTest, TestGetPreviewsURL) {
   };
 
   for (const TestCase& test_case : kTestCases) {
+    base::CommandLine::ForCurrentProcess()->AppendSwitchASCII(
+        data_reduction_proxy::switches::kDataReductionProxyExperiment,
+        test_case.experiment);
+
     base::test::ScopedFeatureList scoped_feature_list;
     scoped_feature_list.InitAndEnableFeatureWithParameters(
         previews::features::kLitePageServerPreviews,
-        {{"previews_host", test_case.previews_host},
-         {"lite_page_preview_experiment", test_case.experiment}});
+        {{"previews_host", test_case.previews_host}});
 
     EXPECT_EQ(PreviewsLitePageNavigationThrottle::GetPreviewsURLForURL(
                   GURL(test_case.original_url)),

components/previews/core/previews_experiments.cc

@@ -219,11 +219,6 @@ GURL GetLitePagePreviewsDomainURL() {
   return GURL("https://litepages.googlezip.net/");
 }
 
-std::string LitePageRedirectPreviewExperiment() {
-  return GetFieldTrialParamValueByFeature(features::kLitePageServerPreviews,
-                                          "lite_page_preview_experiment");
-}
-
 bool IsInLitePageRedirectControl() {
   return base::GetFieldTrialParamByFeatureAsBool(
       features::kLitePageServerPreviews, "control_group", false);

components/previews/core/previews_experiments.h

@@ -123,9 +123,6 @@ size_t LitePageRedirectPreviewMaxNavigationRestarts();
 // The maximum number of seconds to loadshed the Previews server for.
 int PreviewServerLoadshedMaxSeconds();
 
-// The experimental config to send to the previews server.
-std::string LitePageRedirectPreviewExperiment();
-
 // Returns true if we should only report metrics and not trigger when the Lite
 // Page Redirect preview is enabled.
 bool IsInLitePageRedirectControl();