Include Content-Type response header for content:// responses on Android.

Bug: 994326
Change-Id: I199a53fa3325b7cd9d0629ccb7f0d987592f0912
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1756941
Auto-Submit: Eric Roman <eroman@chromium.org>
Reviewed-by: John Abd-El-Malek <jam@chromium.org>
Commit-Queue: Eric Roman <eroman@chromium.org>
Cr-Commit-Position: refs/heads/master@{#688213}

content/browser/android/content_url_loader_factory.cc

@@ -159,7 +159,7 @@ class ContentURLLoader : public network::mojom::URLLoader {
 
     // Set the mimetype of the response.
     GetMimeType(request, path, &head.mime_type);
-    if (!head.mime_type.empty() && head.headers) {
+    if (!head.mime_type.empty()) {
       head.headers = base::MakeRefCounted<net::HttpResponseHeaders>("");
       head.headers->AddHeader(
           base::StringPrintf("%s: %s", net::HttpRequestHeaders::kContentType,