[Downloads] Mark download resumption as disabled by default.

Feature state will be controlled via a server-side field trial.

BUG=7648
BUG=579108

Review URL: https://codereview.chromium.org/1589133003

Cr-Commit-Position: refs/heads/master@{#370138}

content/public/common/content_features.cc

@@ -17,7 +17,7 @@ const base::Feature kBrotliEncoding{"brotli-encoding",
 // Downloads resumption will be controllable via a flag until it's enabled
 // permanently. See https://crbug.com/7648
 const base::Feature kDownloadResumption{"DownloadResumption",
-                                        base::FEATURE_ENABLED_BY_DEFAULT};
+                                        base::FEATURE_DISABLED_BY_DEFAULT};
 
 // The Experimental Framework for controlling access to API experiments.
 const base::Feature kExperimentalFramework{"ExperimentalFramework",