Implement chrome://histograms with network service.

content/browser/webui/web_ui_url_loader_factory.cc

Index: content/browser/webui/web_ui_url_loader_factory.cc
diff --git a/content/browser/webui/web_ui_url_loader_factory.cc b/content/browser/webui/web_ui_url_loader_factory.cc
index fd81d67f161adb79deff6fa5fde05ca5d5712b9b..a6ba11d35876de3c0d4e0d1f947eda9eedc03bac 100644
--- a/content/browser/webui/web_ui_url_loader_factory.cc
+++ b/content/browser/webui/web_ui_url_loader_factory.cc
@@ -15,6 +15,7 @@
 #include "content/browser/blob_storage/chrome_blob_storage_context.h"
 #include "content/browser/frame_host/frame_tree_node.h"
 #include "content/browser/frame_host/render_frame_host_impl.h"
+#include "content/browser/histogram_internals_url_loader.h"
 #include "content/browser/resource_context_impl.h"
 #include "content/browser/webui/url_data_manager_backend.h"
 #include "content/browser/webui/url_data_source_impl.h"
@@ -247,6 +248,9 @@ class WebUIURLLoaderFactory : public mojom::URLLoaderFactory,
               base::Unretained(
                   ChromeBlobStorageContext::GetFor(browser_context_))));
       return;
+    } else if (request.url.host_piece() == kChromeUIHistogramHost) {
+      StartHistogramInternalsURLLoader(request, std::move(client));
+      return;
     }
 
     BrowserThread::PostTask(