add a flag to enable/disable download interception on android

chrome/browser/renderer_host/chrome_resource_dispatcher_host_delegate.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/renderer_host/chrome_resource_dispatcher_host_delegate.h"
 
 #include <stdint.h>
 #include <string>
 #include <utility>
 #include <vector>
@@ skipping 74 matching lines @@
 #include "chrome/browser/supervised_user/supervised_user_resource_throttle.h"
 #endif
 
 #if defined(USE_SYSTEM_PROTOBUF)
 #include <google/protobuf/repeated_field.h>
 #else
 #include "third_party/protobuf/src/google/protobuf/repeated_field.h"
 #endif
 
 #if BUILDFLAG(ANDROID_JAVA_UI)
+#include "base/command_line.h"
+#include "base/metrics/field_trial.h"
 #include "chrome/browser/android/intercept_download_resource_throttle.h"
 #endif
 
 #if defined(OS_ANDROID)
 #include "chrome/browser/renderer_host/data_reduction_proxy_resource_throttle_android.h"
 #include "components/navigation_interception/intercept_navigation_delegate.h"
 #endif
 
 #if defined(ENABLE_DATA_REDUCTION_PROXY_DEBUGGING)
 #include "components/data_reduction_proxy/content/browser/data_reduction_proxy_debug_resource_throttle.h"
@@ skipping 156 matching lines @@
 
   if (crx_id) {
     // We got a component we need to install, so throttle the resource
     // until the component is installed.
     throttles->push_back(
         component_updater::GetOnDemandResourceThrottle(cus, crx_id));
   }
 }
 #endif  // !defined(DISABLE_NACL)
 
+#if BUILDFLAG(ANDROID_JAVA_UI)
+const char kDownloadInterception[] = "EnableDownloadInterception";
+
+bool IsDownloadInterceptionEnabled() {
+  return base::StartsWith(
+      base::FieldTrialList::FindFullName(kDownloadInterception), "Enabled",
+      base::CompareCase::INSENSITIVE_ASCII);

[asanka, 2016/02/11 22:49:20]

Let's move these out to a separate file.

[qinmin, 2016/02/12 00:31:56]

Done. Moved to InterceptDownloadResourceThrottle class.

+}
+#endif  // BUILDFLAG(ANDROID_JAVA_UI)
 }  // namespace
 
 ChromeResourceDispatcherHostDelegate::ChromeResourceDispatcherHostDelegate()
     : download_request_limiter_(g_browser_process->download_request_limiter()),
       safe_browsing_(g_browser_process->safe_browsing_service())
 #if defined(ENABLE_EXTENSIONS)
       , user_script_listener_(new extensions::UserScriptListener())
 #endif
       {
   BrowserThread::PostTask(
@@ skipping 130 matching lines @@
       base::Bind(&NotifyDownloadInitiatedOnUI, child_id, route_id));
 
   // If it's from the web, we don't trust it, so we push the throttle on.
   if (is_content_initiated) {
     const content::ResourceRequestInfo* info =
         content::ResourceRequestInfo::ForRequest(request);
     throttles->push_back(new DownloadResourceThrottle(
         download_request_limiter_, info->GetWebContentsGetterForRequest(),
         request->url(), request->method()));
 #if BUILDFLAG(ANDROID_JAVA_UI)
-    throttles->push_back(
-        new chrome::InterceptDownloadResourceThrottle(
-            request, child_id, route_id, request_id));
+    if (IsDownloadInterceptionEnabled() ||
+        base::CommandLine::ForCurrentProcess()->HasSwitch(
+            switches::kEnableDownloadInterception)) {

[asanka, 2016/02/11 22:49:20]

Why is disabling the default?

Also, if the feature was enabled by the field trial, the user can't override it.

[qinmin, 2016/02/12 00:31:56]

Done. Now the remote server will disable download interception, and locally we
can override that. The default behavior is to always intercept.

+      throttles->push_back(new chrome::InterceptDownloadResourceThrottle(
+          request, child_id, route_id, request_id));
+    }
 #endif
   }
 
   // If this isn't a new request, we've seen this before and added the standard
   //  resource throttles already so no need to add it again.
   if (!request->is_pending()) {
     AppendStandardResourceThrottles(request,
                                     resource_context,
                                     content::RESOURCE_TYPE_MAIN_FRAME,
                                     throttles);
@@ skipping 295 matching lines @@
     return data_reduction_proxy_io_data->ShouldEnableLoFiMode(url_request);
   return false;
 }
 
 // static
 void ChromeResourceDispatcherHostDelegate::
     SetExternalProtocolHandlerDelegateForTesting(
     ExternalProtocolHandler::Delegate* delegate) {
   g_external_protocol_handler_delegate = delegate;
 }