Make shorter api of AppendVariationHeaders and
CreateSimpleURLLoaderWithVariationHeaders.

Tons of people call AppendVariationHeaders() with variations::SignedIn::kNo with
the following comment:
  // Note: It's OK to pass SignedIn::kNo if it's unknown, as it does not affect
  // transmission of experiments coming from the variations server.
This CL simply make a version without the sign-in parameter of
AppendVariationHeaders and CreateSimpleULRLoaderWithVariationHeader and remove
those many comments in the code.

BUG=857127

Cq-Include-Trybots: luci.chromium.try:ios-simulator-full-configs;master.tryserver.chromium.mac:ios-simulator-cronet
Change-Id: Id0af5394ce31b117e109033f44a43720d4407197
Reviewed-on: https://chromium-review.googlesource.com/1121669
Commit-Queue: Theresa <[email protected]>
Reviewed-by: Theresa <[email protected]>
Reviewed-by: Zachary Kuznia <[email protected]>
Reviewed-by: Marc Treib <[email protected]>
Reviewed-by: Matt Menke <[email protected]>
Reviewed-by: Nicolas Zea <[email protected]>
Reviewed-by: Vaclav Brozek <[email protected]>
Reviewed-by: Mark Cogan <[email protected]>
Reviewed-by: Stepan Khapugin <[email protected]>
Reviewed-by: Samuel Huang <[email protected]>
Reviewed-by: Mathieu Perreault <[email protected]>
Reviewed-by: Alexei Svitkine <[email protected]>
Reviewed-by: Mark Pearson <[email protected]>
Cr-Commit-Position: refs/heads/master@{#573534}
diff --git a/components/variations/net/variations_http_headers.h b/components/variations/net/variations_http_headers.h
index bb3df85..f7c783e 100644
--- a/components/variations/net/variations_http_headers.h
+++ b/components/variations/net/variations_http_headers.h
@@ -41,6 +41,12 @@
                             SignedIn signed_in,
                             net::HttpRequestHeaders* headers);
 
+// Adds Chrome experiment and metrics state as custom headers to |headers|
+// when the signed-in state is not known to the caller; See above for details.
+bool AppendVariationHeadersUnknownSignedIn(const GURL& url,
+                                           InIncognito incognito,
+                                           net::HttpRequestHeaders* headers);
+
 // Returns the HTTP header names which are added by AppendVariationHeaders().
 std::set<std::string> GetVariationHeaderNames();
 
@@ -60,6 +66,15 @@
     SignedIn signed_in,
     const net::NetworkTrafficAnnotationTag& annotation_tag);
 
+// Creates a SimpleURLLoader that will include variations headers for requests
+// to Google when the signed-in state is unknown and ensures they're removed
+// if a redirect to a non-Google URL occurs.
+std::unique_ptr<network::SimpleURLLoader>
+CreateSimpleURLLoaderWithVariationsHeadersUnknownSignedIn(
+    std::unique_ptr<network::ResourceRequest> request,
+    InIncognito incognito,
+    const net::NetworkTrafficAnnotationTag& annotation_tag);
+
 namespace internal {
 
 // Checks whether variation headers should be appended to requests to the