Add DCHECK for chrome-proxy header in previews handler

Bug: 1011457
Change-Id: I2ce266270a5189bb3dc4d09de2d193b3d0737209
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1846042Reviewed-by: Tarun Bansal <tbansal@chromium.org>
Commit-Queue: Robert Ogden <robertogden@chromium.org>
Cr-Commit-Position: refs/heads/master@{#704241}

chrome/browser/previews/previews_lite_page_redirect_url_loader.cc

@@ -12,6 +12,7 @@
 #include "base/strings/stringprintf.h"
 #include "chrome/browser/previews/previews_lite_page_redirect_url_loader_interceptor.h"
 #include "chrome/browser/profiles/profile.h"
+#include "components/data_reduction_proxy/core/browser/data_reduction_proxy_request_options.h"
 #include "components/previews/core/previews_experiments.h"
 #include "components/previews/core/previews_lite_page_redirect.h"
 #include "content/public/browser/browser_context.h"
@@ -130,6 +131,9 @@ void PreviewsLitePageRedirectURLLoader::StartRedirectToPreview(
         network_loader_factory,
     int frame_tree_node_id) {
   DCHECK_CALLED_ON_VALID_SEQUENCE(sequence_checker_);
+  DCHECK(data_reduction_proxy::DataReductionProxyRequestOptions::
+             GetSessionKeyFromRequestHeaders(chrome_proxy_headers)
+                 .has_value());
 
   GURL original_url = modified_resource_request_.url;
   GURL lite_page_url =

chrome/browser/previews/previews_lite_page_redirect_url_loader_interceptor.cc

@@ -9,6 +9,7 @@
 #include <utility>
 
 #include "base/bind.h"
+#include "base/command_line.h"
 #include "base/metrics/histogram_macros.h"
 #include "base/optional.h"
 #include "base/stl_util.h"
@@ -71,8 +72,14 @@ net::HttpRequestHeaders GetChromeProxyHeaders(
     uint64_t page_id) {
   net::HttpRequestHeaders headers;
   // Return empty headers for unittests.
-  if (!browser_context)
+  if (!browser_context) {
+    if (base::CommandLine::ForCurrentProcess()->HasSwitch(
+            "add-chrome-proxy-header-for-lpr-tests")) {
+      headers.SetHeader(data_reduction_proxy::chrome_proxy_header(),
+                        "s=secret");
+    }
     return headers;
+  }
 
   auto* settings =
       DataReductionProxyChromeSettingsFactory::GetForBrowserContext(

chrome/browser/previews/previews_lite_page_redirect_url_loader_interceptor_unittest.cc

@@ -74,6 +74,9 @@ class PreviewsLitePageRedirectURLLoaderInterceptorTest : public testing::Test {
   void TearDown() override {}
 
   void SetUp() override {
+    base::CommandLine::ForCurrentProcess()->AppendSwitch(
+        "add-chrome-proxy-header-for-lpr-tests");
+
     interceptor_ =
         std::make_unique<PreviewsLitePageRedirectURLLoaderInterceptor>(
             shared_factory_, 1, 2);