Bundle DidOverscrollParams with the input event ack

Currently, overscroll notifications are always sent as a separate IPC message,
regardless of the causal event.  Instead, bundle the overscroll metadata with
the event ack if the event caused the overscroll, saving an IPC message in the
most common overscroll case.

BUG=328503

Review URL: https://codereview.chromium.org/281723010

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@271541 0039d316-1c4b-4281-b951-d872f2087c98

1 files changed, 35 insertions, 0 deletions

diff --git a/ipc/ipc_message_utils.h b/ipc/ipc_message_utils.h
index 102992d..6bfd103 100644
--- a/ipc/ipc_message_utils.h
+++ b/ipc/ipc_message_utils.h
@@ -14,6 +14,7 @@
 #include "base/containers/small_map.h"
 #include "base/files/file.h"
 #include "base/format_macros.h"
+#include "base/memory/scoped_ptr.h"
 #include "base/memory/scoped_vector.h"
 #include "base/strings/string16.h"
 #include "base/strings/string_util.h"
@@ -706,6 +707,40 @@ struct ParamTraits<base::SmallMap<NormalMap, kArraySize, EqualKey, MapInit> > {
   }
 };
 
+template <class P>
+struct ParamTraits<scoped_ptr<P> > {
+  typedef scoped_ptr<P> param_type;
+  static void Write(Message* m, const param_type& p) {
+    bool valid = !!p;
+    WriteParam(m, valid);
+    if (valid)
+      WriteParam(m, *p);
+  }
+  static bool Read(const Message* m, PickleIterator* iter, param_type* r) {
+    bool valid = false;
+    if (!ReadParam(m, iter, &valid))
+      return false;
+
+    if (!valid) {
+      r->reset();
+      return true;
+    }
+
+    param_type temp(new P());
+    if (!ReadParam(m, iter, temp.get()))
+      return false;
+
+    r->swap(temp);
+    return true;
+  }
+  static void Log(const param_type& p, std::string* l) {
+    if (p)
+      LogParam(*p, l);
+    else
+      l->append("NULL");
+  }
+};
+
 // IPC types ParamTraits -------------------------------------------------------
 
 // A ChannelHandle is basically a platform-inspecific wrapper around the