add a flag to enable/disable download interception on android

chrome/browser/android/intercept_download_resource_throttle.cc

Index: chrome/browser/android/intercept_download_resource_throttle.cc
diff --git a/chrome/browser/android/intercept_download_resource_throttle.cc b/chrome/browser/android/intercept_download_resource_throttle.cc
index 1592233f81895c4a8ad36a5e77f949d2378b0100..1cedf9e2c3b53a7a9440062f95cef26cedf166d7 100644
--- a/chrome/browser/android/intercept_download_resource_throttle.cc
+++ b/chrome/browser/android/intercept_download_resource_throttle.cc
@@ -4,7 +4,11 @@
 
 #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"
@@ -14,6 +18,9 @@
 
 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.
@@ -41,6 +48,24 @@ void RecordInterceptFailureReasons(
 
 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),
+      "Enabled", base::CompareCase::INSENSITIVE_ASCII);
+}
+
 InterceptDownloadResourceThrottle::InterceptDownloadResourceThrottle(
     net::URLRequest* request,
     int render_process_id,