Add flag for blocking insecure downloads on secure pages.

This CL adds a feature flag that will be used, when enabled, to treat
executable file types as active content. Once implemented, that will
result in silent blocking of executable downloads if served insecurely.
This CL is just the flag, and application logic will come later.

Change-Id: I0f90344a31cdade1b64dbe2adc82165891e8387c
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1597632
Reviewed-by: Christopher Thompson <[email protected]>
Commit-Queue: Joe DeBlasio <[email protected]>
Cr-Commit-Position: refs/heads/master@{#657035}
diff --git a/chrome/browser/about_flags.cc b/chrome/browser/about_flags.cc
index 9da0fd9..f2b7fa2 100644
--- a/chrome/browser/about_flags.cc
+++ b/chrome/browser/about_flags.cc
@@ -3138,6 +3138,11 @@
          network::switches::kUnsafelyTreatInsecureOriginAsSecure,
          "")},
 
+    {"treat-unsafe-downloads-as-active-content",
+     flag_descriptions::kTreatUnsafeDownloadsAsActiveName,
+     flag_descriptions::kTreatUnsafeDownloadsAsActiveDescription, kOsDesktop,
+     FEATURE_VALUE_TYPE(features::kTreatUnsafeDownloadsAsActive)},
+
 #if defined(OS_CHROMEOS)
     {"enable-play-store-search", flag_descriptions::kEnablePlayStoreSearchName,
      flag_descriptions::kEnablePlayStoreSearchDescription, kOsCrOS,