add a flag to enable/disable download interception on android

chrome/browser/android/intercept_download_resource_throttle.cc

 // Copyright (c) 2012 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 "chrome/browser/android/intercept_download_resource_throttle.h"
 
+#include "base/command_line.h"
+#include "base/metrics/field_trial.h"
 #include "base/metrics/histogram_macros.h"
+#include "base/strings/string_util.h"
+#include "chrome/common/chrome_switches.h"
 #include "components/data_reduction_proxy/core/common/data_reduction_proxy_headers.h"
 #include "content/public/browser/android/download_controller_android.h"
 #include "content/public/browser/resource_controller.h"
 #include "net/http/http_request_headers.h"
 #include "net/http/http_response_headers.h"
 #include "net/url_request/url_request.h"
 
 namespace {
 
+// Finch flag to be passed in.
+const char kDisableDownloadInterception[] = "DisableDownloadInterception";
+
 // UMA histogram for tracking reasons that chrome fails to intercept the
 // download. Keep this in sync with MobileDownloadInterceptFailureReasons in
 // histograms.xml.
 enum MobileDownloadInterceptFailureReason {
   NO_FAILURE = 0,
   EMPTY_URL,
   NON_HTTP_OR_HTTPS,
   NON_GET_METHODS,
   NO_REQUEST_HEADERS,
   USE_HTTP_AUTH,
   USE_CHANNEL_BOUND_COOKIES,
   // FAILURE_REASON_SIZE should always be last - this is a count of the number
   // of items in this enum.
   FAILURE_REASON_SIZE,
 };
 
 void RecordInterceptFailureReasons(
     MobileDownloadInterceptFailureReason reason) {
   UMA_HISTOGRAM_ENUMERATION("MobileDownload.InterceptFailureReason",
                             reason,
                             FAILURE_REASON_SIZE);
 }
 
 }  // namespace
 
 namespace chrome {
 
+// static
+bool InterceptDownloadResourceThrottle::IsDownloadInterceptionEnabled() {
+
+  if (base::CommandLine::ForCurrentProcess()->HasSwitch(
+      switches::kEnableDownloadInterception)) {
+    return true;
+  }
+
+  if (base::CommandLine::ForCurrentProcess()->HasSwitch(
+      switches::kDisableDownloadInterception)) {
+    return false;
+  }
+
+  return !base::StartsWith(
+      base::FieldTrialList::FindFullName(kDisableDownloadInterception),

[asanka, 2016/02/23 02:55:30]

See base/feature_list.h . Rather than add the enable/disable flags, you should
consider using the Features API. This way you'll be able to control the behavior
both on the command line and via a field trial.

[qinmin, 2016/02/23 22:28:05]

Done.

+      "Enabled", base::CompareCase::INSENSITIVE_ASCII);
+}
+
 InterceptDownloadResourceThrottle::InterceptDownloadResourceThrottle(
     net::URLRequest* request,
     int render_process_id,
     int render_view_id,
     int request_id)
     : request_(request),
       render_process_id_(render_process_id),
       render_view_id_(render_view_id),
       request_id_(request_id) {
 }
 
 InterceptDownloadResourceThrottle::~InterceptDownloadResourceThrottle() {
 }
 
 void InterceptDownloadResourceThrottle::WillProcessResponse(bool* defer) {
   ProcessDownloadRequest();
 }
 
 const char* InterceptDownloadResourceThrottle::GetNameForLogging() const {
   return "InterceptDownloadResourceThrottle";
 }
 
 void InterceptDownloadResourceThrottle::ProcessDownloadRequest() {
+  if (!IsDownloadInterceptionEnabled())
+    return;
+
   if (request_->url_chain().empty()) {
     RecordInterceptFailureReasons(EMPTY_URL);
     return;
   }
 
   GURL url = request_->url_chain().back();
   if (!url.SchemeIsHTTPOrHTTPS()) {
     RecordInterceptFailureReasons(NON_HTTP_OR_HTTPS);
     return;
   }
@@ skipping 31 matching lines @@
     return;
   }
 
   content::DownloadControllerAndroid::Get()->CreateGETDownload(
       render_process_id_, render_view_id_, request_id_);
   controller()->Cancel();
   RecordInterceptFailureReasons(NO_FAILURE);
 }
 
 }  // namespace chrome