Give |allow_stale_resources_| a lower priority in DetermineRevalidationPolicy

This CL changes DetermineRevalidationPolicy a bit to simplify it. With this
CL, |allow_stale_resources_| will be checked after
ResourceLoaderOptions::CanReuseRequest is checked. CanReuseRequest checks
the synchronous policy and the cors policy, and neither of them is related
to staleness. Moreover, the synchronous policy was once checked BEFORE
allow_stale_resources_ (see [1]). Also, any user of
ResourceCacheValidationSuppressor, the class used to enable
|allow_stale_resource_|, doesn't seem to be interested in CORS. Hence I expect
no behavior change from this CL.

1: https://crrev.com/733a476495c43c1f472e5770c9d8aeeb94c5caca

BUG=652228
R=hiroshige@chromium.org, japhet@chromium.org

Review-Url: https://codereview.chromium.org/2828243002
Cr-Commit-Position: refs/heads/master@{#466880}

third_party/WebKit/Source/platform/loader/fetch/ResourceFetcher.cpp

@@ -923,10 +923,6 @@ ResourceFetcher::DetermineRevalidationPolicy(
     return kReload;
   }
 
-  // Don't reload resources while pasting.
-  if (allow_stale_resources_)
-    return kUse;
-
   if (!fetch_params.Options().CanReuseRequest(existing_resource->Options()))
     return kReload;
 
@@ -934,6 +930,10 @@ ResourceFetcher::DetermineRevalidationPolicy(
   if (existing_resource->IsPreloaded())
     return kUse;
 
+  // Don't reload resources while pasting.
+  if (allow_stale_resources_)
+    return kUse;
+
   // WebCachePolicy::ReturnCacheDataElseLoad uses the cache no matter what.
   if (request.GetCachePolicy() == WebCachePolicy::kReturnCacheDataElseLoad)
     return kUse;