Reduce/remove usage of BrowserThread in content/browser/loader.

content/browser/loader/async_resource_handler_unittest.cc

Index: content/browser/loader/async_resource_handler_unittest.cc
diff --git a/content/browser/loader/async_resource_handler_unittest.cc b/content/browser/loader/async_resource_handler_unittest.cc
index 33d6b87a147b46704a7a06863f5f6ece8949fd37..27ea0db6de52d0b213cd9a0eb5191579cd4cc2cb 100644
--- a/content/browser/loader/async_resource_handler_unittest.cc
+++ b/content/browser/loader/async_resource_handler_unittest.cc
@@ -101,7 +101,8 @@ class RecordingResourceMessageFilter : public ResourceMessageFilter {
             nullptr,
             nullptr,
             base::Bind(&RecordingResourceMessageFilter::GetContexts,
-                       base::Unretained(this))),
+                       base::Unretained(this)),
+            BrowserThread::GetTaskRunnerForThread(BrowserThread::IO)),
         resource_context_(resource_context),
         request_context_(request_context) {
     InitializeForTest();