Add a new flag to allow download without strong validators to resume

This CL adds a new flag to allow download without strong validators to
resume. Some data will be used for validation purpose.
Two browser tests are added.

BUG=965215

Change-Id: Ia6a86dfbe2c076b5123a909142e47b80192cb80c
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1635830
Commit-Queue: Min Qin <[email protected]>
Reviewed-by: Xing Liu <[email protected]>
Cr-Commit-Position: refs/heads/master@{#664607}
diff --git a/chrome/browser/about_flags.cc b/chrome/browser/about_flags.cc
index d9a5bfc..6213bdf0 100644
--- a/chrome/browser/about_flags.cc
+++ b/chrome/browser/about_flags.cc
@@ -2746,6 +2746,13 @@
      FEATURE_VALUE_TYPE(chrome::android::kDownloadRename)},
 #endif
 
+    {"download-resumption-without-strong-validators",
+     flag_descriptions::kDownloadResumptionWithoutStrongValidatorsName,
+     flag_descriptions::kDownloadResumptionWithoutStrongValidatorsDescription,
+     kOsAll,
+     FEATURE_VALUE_TYPE(
+         download::features::kAllowDownloadResumptionWithoutStrongValidators)},
+
 #if defined(OS_ANDROID)
     {"new-net-error-page-ui", flag_descriptions::kNewNetErrorPageUIName,
      flag_descriptions::kNewNetErrorPageUIDescription, kOsAndroid,