Implement chrome://histograms with network service.

content/browser/histogram_internals_url_loader.cc

+// Copyright 2017 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "content/browser/histogram_internals_url_loader.h"
+
+#include "base/metrics/histogram_macros.h"
+#include "base/metrics/statistics_recorder.h"
+#include "content/browser/histogram_internals_request_job.h"
+#include "mojo/common/data_pipe_utils.h"
+
+namespace content {
+
+void StartHistogramInternalsURLLoader(const ResourceRequest& request,
+                                      mojom::URLLoaderClientPtr client) {
+  scoped_refptr<net::HttpResponseHeaders> headers(
+      new net::HttpResponseHeaders("HTTP/1.1 200 OK"));
+  ResourceResponseHead resource_response;
+  resource_response.headers = headers;
+  resource_response.mime_type = "text/html";
+  client->OnReceiveResponse(resource_response, base::nullopt, nullptr);
+
+  base::StatisticsRecorder::ImportProvidedHistograms();
+  std::string data = HistogramInternalsRequestJob::GenerateHTML(request.url);
+
+  MojoCreateDataPipeOptions options;
+  options.struct_size = sizeof(MojoCreateDataPipeOptions);
+  options.flags = MOJO_CREATE_DATA_PIPE_OPTIONS_FLAG_NONE;
+  options.element_num_bytes = 1;
+  options.capacity_num_bytes = data.size();
+  mojo::DataPipe data_pipe(options);
+
+  DCHECK(data_pipe.producer_handle.is_valid());
+  DCHECK(data_pipe.consumer_handle.is_valid());
+
+  CHECK(mojo::common::BlockingCopyFromString(data, data_pipe.producer_handle));
+
+  client->OnStartLoadingResponseBody(std::move(data_pipe.consumer_handle));
+
+  ResourceRequestCompletionStatus request_complete_data;
+  request_complete_data.error_code = net::OK;
+  request_complete_data.exists_in_cache = false;
+  request_complete_data.completion_time = base::TimeTicks::Now();
+  request_complete_data.encoded_data_length = data.size();
+  request_complete_data.encoded_body_length = data.size();
+  client->OnComplete(request_complete_data);
+}
+
+}  // namespace content