Change Lo-Fi bool to bitmask to support multiple Previews types

chrome/browser/loader/chrome_resource_dispatcher_host_delegate.h

Index: chrome/browser/loader/chrome_resource_dispatcher_host_delegate.h
diff --git a/chrome/browser/loader/chrome_resource_dispatcher_host_delegate.h b/chrome/browser/loader/chrome_resource_dispatcher_host_delegate.h
index 195453bb8e67eb05451a0858d01e13525f0eb1d6..31a101fc4441111fbff9f84d3e012a384a9bfb5d 100644
--- a/chrome/browser/loader/chrome_resource_dispatcher_host_delegate.h
+++ b/chrome/browser/loader/chrome_resource_dispatcher_host_delegate.h
@@ -14,6 +14,7 @@
 #include "base/memory/ref_counted.h"
 #include "chrome/browser/external_protocol/external_protocol_handler.h"
 #include "content/public/browser/resource_dispatcher_host_delegate.h"
+#include "content/public/common/previews_state.h"
 #include "extensions/features/features.h"
 
 class DownloadRequestLimiter;
@@ -82,7 +83,7 @@ class ChromeResourceDispatcherHostDelegate
                            content::ResourceContext* resource_context,
                            content::ResourceResponse* response) override;
   void RequestComplete(net::URLRequest* url_request) override;
-  bool ShouldEnableLoFiMode(
+  content::PreviewsState GetPreviewsState(

[Nico, 2017/01/09 22:35:03]

I'm confused about this. The enum definition looks like the states are mutually
exclusive and this returns the enum and not an unsigned, yet the CL description
says "bitmask" and the checks use & instead of ==. Is this a bitmask, or no?

[megjablon, 2017/01/10 22:30:01]

The states aren't mutually exclusive. Server Lo-Fi and client Lo-Fi can both be
enabled at the same time. That's what this change is to help with. We need to
move Lo-Fi under Previews as a type, but also allow multiple previews types to
be set at once. This was initially an int, but nasko asked for me to use the
type, and I've seen it done both ways throughout the code. 

[Nico, 2017/01/11 01:14:47]

I think some integer type is more natural for a bit mask, but ok. Add a comment
"Returns bitmask of potentially several PreviewsState comment" then maybe.

[megjablon, 2017/01/12 17:56:29]

Done.

       const net::URLRequest& url_request,
       content::ResourceContext* resource_context) override;
   content::NavigationData* GetNavigationData(