[downloads] Set initiator when handling downloads via a[download]

content/common/frame_messages.h

Index: content/common/frame_messages.h
diff --git a/content/common/frame_messages.h b/content/common/frame_messages.h
index 64bf4d7a1af75a70eb37dddc37a7598a008848fa..b4863c49399df5c5fb7d559c233e663be4343344 100644
--- a/content/common/frame_messages.h
+++ b/content/common/frame_messages.h
@@ -37,6 +37,7 @@
 #include "content/public/common/javascript_message_type.h"
 #include "content/public/common/page_importance_signals.h"
 #include "content/public/common/page_state.h"
+#include "content/public/common/referrer.h"
 #include "content/public/common/resource_response.h"
 #include "content/public/common/stop_find_action.h"
 #include "content/public/common/three_d_api_types.h"
@@ -424,6 +425,15 @@ IPC_STRUCT_BEGIN(FrameHostMsg_OpenURL_Params)
   IPC_STRUCT_MEMBER(bool, is_history_navigation_in_new_child)
 IPC_STRUCT_END()
 
+IPC_STRUCT_BEGIN(FrameHostMsg_DownloadUrl_Params)
+  IPC_STRUCT_MEMBER(int, render_view_id)
+  IPC_STRUCT_MEMBER(int, render_frame_id)
+  IPC_STRUCT_MEMBER(GURL, url)
+  IPC_STRUCT_MEMBER(content::Referrer, referrer)
+  IPC_STRUCT_MEMBER(url::Origin, initiator_origin)

[clamy, 2016/12/14 16:25:38]

Should this be an Optional<url::Origin>, considering that it will be put in an
Optional<url::Origin> and that we're setting all initiators transmitted from the
renderer as optional?

[asanka, 2016/12/14 18:21:30]

The intent is that URLRequest::initiator() and in turn
DownloadUrlParameters::initiator() can be optional, but DownloadUrl requests
coming from a renderer *must* have an initiator_origin. If one is unavailable,
we'd end up with a unique origin which has subtly different semantics than a
null origin. I.e. a unique initiator would result in no SameSite cookies being
sent while a null initiator may result in SameSite=Lax cookies being sent for
safe methods.

mkwest: Is the above reasonable? Should a renderer be able to initiate a
download with a null initiator origin? I intentionally made it not so.

There are other users of the DownloadUrlParameters API (a.k.a.
DownloadManager::DownloadURL() API). These should be able to make requests
without specifying an initiator since there may not always be one. E.g. a
programmatic download initiated by Chrome itself wouldn't have an initiator
origin.

+  IPC_STRUCT_MEMBER(base::string16, suggested_name)
+IPC_STRUCT_END()
+
 IPC_STRUCT_BEGIN(FrameMsg_TextTrackSettings_Params)
   // Text tracks on/off state
   IPC_STRUCT_MEMBER(bool, text_tracks_enabled)
@@ -1029,12 +1039,7 @@ IPC_MESSAGE_ROUTED1(FrameHostMsg_DidFinishLoad,
                     GURL /* validated_url */)
 
 // Initiates a download based on user actions like 'ALT+click'.
-IPC_MESSAGE_CONTROL5(FrameHostMsg_DownloadUrl,
-                     int /* render_view_id */,
-                     int /* render_frame_id */,
-                     GURL /* url */,
-                     content::Referrer /* referrer */,
-                     base::string16 /* suggested_name */)
+IPC_MESSAGE_CONTROL(FrameHostMsg_DownloadUrl, FrameHostMsg_DownloadUrl_Params)
 
 // Asks the browser to save a image (for <canvas> or <img>) from a data URL.
 // Note: |data_url| is the contents of a data:URL, and that it's represented as