SelectionOwner: add support for TIMESTAMP target

ui/base/x/selection_owner.cc

Index: ui/base/x/selection_owner.cc
diff --git a/ui/base/x/selection_owner.cc b/ui/base/x/selection_owner.cc
index 170f32e19b2c0ea71e90bdb53e9386c5aea26fb0..a8521c4442b55a507530f080461cbc6c50273eb6 100644
--- a/ui/base/x/selection_owner.cc
+++ b/ui/base/x/selection_owner.cc
@@ -12,6 +12,7 @@
 #include "ui/base/x/selection_utils.h"
 #include "ui/base/x/x11_foreign_window_manager.h"
 #include "ui/base/x/x11_util.h"
+#include "ui/events/platform/x11/x11_event_source.h"
 
 namespace ui {
 
@@ -22,15 +23,10 @@ const char kIncr[] = "INCR";
 const char kMultiple[] = "MULTIPLE";
 const char kSaveTargets[] = "SAVE_TARGETS";
 const char kTargets[] = "TARGETS";
+const char kTimestamp[] = "TIMESTAMP";
 
-const char* kAtomsToCache[] = {
-  kAtomPair,
-  kIncr,
-  kMultiple,
-  kSaveTargets,
-  kTargets,
-  NULL
-};
+const char* kAtomsToCache[] = {kAtomPair, kIncr,      kMultiple, kSaveTargets,
+                               kTargets,  kTimestamp, NULL};
 
 // The period of |incremental_transfer_abort_timer_|. Arbitrary but must be <=
 // than kIncrementalTransferTimeoutMs.
@@ -122,6 +118,12 @@ void SelectionOwner::RetrieveTargets(std::vector<XAtom>* targets) {
 
 void SelectionOwner::TakeOwnershipOfSelection(
     const SelectionFormatMap& data) {
+  // Save the last server timestamp seen from X, to satisfy requests for the
+  // TIMESTAMP target later…
+  acquired_selection_timestamp_ =
+      X11EventSource::GetInstance()->last_seen_server_time();
+  // …but always pass CurrentTime to XSetSelectionOwner to increase the chances
+  // of this succeeding.
   XSetSelectionOwner(x_display_, selection_name_, x_window_, CurrentTime);

[dcheng, 2016/04/20 00:55:26]

For whatever reason, using last_seen_server_time() causes XSetSelectionOwner()
to fail randomly. So even though we grab a timestamp from X, we always pass
CurrentTime here to make it more likely that it will succeed.

 
   if (XGetSelectionOwner(x_display_, selection_name_) == x_window_) {
@@ -219,14 +221,21 @@ bool SelectionOwner::ProcessTarget(XAtom target,
   XAtom multiple_atom = atom_cache_.GetAtom(kMultiple);
   XAtom save_targets_atom = atom_cache_.GetAtom(kSaveTargets);
   XAtom targets_atom = atom_cache_.GetAtom(kTargets);
+  XAtom timestamp_atom = atom_cache_.GetAtom(kTimestamp);
 
   if (target == multiple_atom || target == save_targets_atom)
     return false;
 
-  if (target == targets_atom) {
+  if (target == timestamp_atom) {
+    XChangeProperty(
+        x_display_, requestor, property, XA_INTEGER, 32, PropModeReplace,
+        reinterpret_cast<unsigned char*>(&acquired_selection_timestamp_), 1);
+    return true;
+  } else if (target == targets_atom) {
     // We have been asked for TARGETS. Send an atom array back with the data
     // types we support.
     std::vector<XAtom> targets;
+    targets.push_back(timestamp_atom);
     targets.push_back(targets_atom);
     targets.push_back(save_targets_atom);
     targets.push_back(multiple_atom);