Implement ui::ClipboardMus.

components/mus/public/interfaces/clipboard.mojom

Index: components/mus/public/interfaces/clipboard.mojom
diff --git a/components/mus/public/interfaces/clipboard.mojom b/components/mus/public/interfaces/clipboard.mojom
index 0e7c67581a94e5e1a448925c3b3641f834cd8db9..b483cab31a18a67604869f16a026920d133614bc 100644
--- a/components/mus/public/interfaces/clipboard.mojom
+++ b/components/mus/public/interfaces/clipboard.mojom
@@ -4,6 +4,14 @@
 
 module mus.mojom;
 
+const string MIME_TYPE_HTML = "text/html";
+const string MIME_TYPE_MOZ_URL = "text/x-moz-url";
+const string MIME_TYPE_PNG = "image/png";
+const string MIME_TYPE_RTF = "text/rtf";
+const string MIME_TYPE_TEXT = "text/plain";
+const string MIME_TYPE_URI_LIST = "text/uri-list";
+const string MIME_TYPE_URL = "text/url";
+
 interface Clipboard {
   enum Type {
     COPY_PASTE = 0,
@@ -11,11 +19,6 @@ interface Clipboard {
     DRAG = 2
   };
 
-  // Mime type constants
-  const string MIME_TYPE_TEXT = "text/plain";
-  const string MIME_TYPE_HTML = "text/html";
-  const string MIME_TYPE_URL = "text/url";
-
   // Returns a sequence number which uniquely identifies clipboard state.
   // Clients are able to assume that the clipboard contents are unchanged as
   // long as this number has not changed. This number is monotonically
@@ -29,17 +32,14 @@ interface Clipboard {
   GetAvailableMimeTypes(Type clipboard_types)
       => (uint64 sequence, array<string> types);
 
-  // If the current sequence number is still |sequence|, returns true and the
-  // current data associated with the requested Mime type. When the sequence
-  // number has changed (because new data has been written to the clipboard),
-  // returns false and null for |data|.
+  // Returns the current data associated with the requested Mime type.
   //
   // We don't want to provide one API to return the entire clipboard state
   // because the combined size of the clipboard can be megabytes, especially
   // when image data is involved.
   [Sync]
-  ReadMimeType(uint64 sequence, Type clipboard_type, string mime_type)
-      => (bool sequence_valid, array<uint8>? data);
+  ReadMimeType(Type clipboard_type, string mime_type)

[sky, 2016/05/26 23:10:26]

WDYT of renaming to ReadClipboardData? That better matches WriteClipboardData.

How come you removed the sequence number? It seems like if read doesn't have a
sequence number there isn't much value in the sequence number. But I could
certainly be wrong.

[Elliot Glaysher, 2016/05/31 17:01:40]

Done.
Looking at the underlying interface, this isn't how it works. Webkit and PPAPI
read the sequence number, read a bunch of objects, and then read the sequence
number again to make sure that the underlying clipboard hasn't changed.

If I was starting from scratch, I agree that moving the sequence number to read
would be much better design. As ui::Clipboard is written today, we don't have a
sequence number to send as part of the read call, and doing an additional sync
call isn't good.

I've added back the sequence number as a return value for future users who are
more clever, though it's ignored in the current ui::ClipboardMus implementation.

[dcheng, 2016/05/31 17:46:46]

I haven't had time to look over this patch yet, but the reason Blink (and
probably PPAPI, since it was written based on what Blink did at the time) does
that is largely historical. I would support changing this. Seems a bit out of
scope for this particular patch though.

+      => (array<uint8>? data);
 
   // Writes a set of mime types to the clipboard. This will increment the
   // sequence number and return that. In the case of an empty or null map,