Move MimeTypeResourceHandler before ThrottlingResourceHandler

content/browser/loader/resource_dispatcher_host_impl.cc

Index: content/browser/loader/resource_dispatcher_host_impl.cc
diff --git a/content/browser/loader/resource_dispatcher_host_impl.cc b/content/browser/loader/resource_dispatcher_host_impl.cc
index 11c590b98aa2bec8ae5c790b2321705d30bdfee8..efa9d85b5565c27d293f169fe47428ff767281b2 100644
--- a/content/browser/loader/resource_dispatcher_host_impl.cc
+++ b/content/browser/loader/resource_dispatcher_host_impl.cc
@@ -49,7 +49,8 @@
 #include "content/browser/loader/async_revalidation_manager.h"
 #include "content/browser/loader/cross_site_resource_handler.h"
 #include "content/browser/loader/detachable_resource_handler.h"
-#include "content/browser/loader/mime_type_resource_handler.h"
+#include "content/browser/loader/intercepting_resource_handler.h"
+#include "content/browser/loader/mime_sniffing_resource_handler.h"
 #include "content/browser/loader/navigation_resource_handler.h"
 #include "content/browser/loader/navigation_resource_throttle.h"
 #include "content/browser/loader/navigation_url_loader_impl_core.h"
@@ -1686,9 +1687,12 @@ ResourceDispatcherHostImpl::AddStandardHandlers(
 #if defined(ENABLE_PLUGINS)
   plugin_service = PluginService::GetInstance();
 #endif
-  // Insert a buffered event handler before the actual one.
-  handler.reset(new MimeTypeResourceHandler(std::move(handler), this,
-                                            plugin_service, request));
+
+  // The InterceptingResourceHandler will replace its next handler with an
+  // appropriate one based on the MIME type of the response if needed. It
+  // should be placed at the end of the chain, just before |handler|.
+  handler.reset(new InterceptingResourceHandler(std::move(handler), this,
+                                                plugin_service, request));
 
   ScopedVector<ResourceThrottle> throttles;
 
@@ -1720,6 +1724,9 @@ ResourceDispatcherHostImpl::AddStandardHandlers(
   handler.reset(new ThrottlingResourceHandler(std::move(handler), request,
                                               std::move(throttles)));
 
+  // Insert a buffered event handler to sniff the mime type first.
+  handler.reset(new MimeSniffingResourceHandler(std::move(handler), request));

[asanka, 2016/06/23 02:30:13]

Note that this ResourceHandler is special. Every resource handler behind it has
to be prepared to service OnWillRead *before* OnResponseStarted. It used to be
an exception that only the last ResourceHandler needed to handle, but it's now
the norm for all ResourceHandlers due to MimeSniffingResourceHandler being at
the head of the chain.

Maybe we should document it.

[clamy, 2016/06/28 16:20:41]

Added documentation about this behavior in the comment.

+
   return handler;
 }