Add UMA statistics to the clipboard

ui/base/clipboard/clipboard.h

Index: ui/base/clipboard/clipboard.h
diff --git a/ui/base/clipboard/clipboard.h b/ui/base/clipboard/clipboard.h
index ae7216528f4d8ef818e8888a9d79d141023b4aeb..1f5cf201ed12b2d4487d4a773a5fa236bf61720d 100644
--- a/ui/base/clipboard/clipboard.h
+++ b/ui/base/clipboard/clipboard.h
@@ -173,6 +173,8 @@ class UI_EXPORT Clipboard : NON_EXPORTED_BASE(public base::ThreadChecker) {
   // WriteObject() caller can use the SourceTag that will be stored in the
   // clipboard. NULL value means "no tag".
   typedef void* SourceTag;
+  // kInvalidSourceTag is not NULL but a special value != any pointer.
+  static const SourceTag kInvalidSourceTag;
   static ObjectMapParam SourceTag2Binary(SourceTag tag);
   static SourceTag Binary2SourceTag(const std::string& serialization);
 
@@ -355,6 +357,15 @@ class UI_EXPORT Clipboard : NON_EXPORTED_BASE(public base::ThreadChecker) {
                  size_t data_len);
 
   void WriteSourceTag(SourceTag tag);
+
+  enum TrackedAction {
+    WRITE_CLIPBOARD_NO_SOURCE_TAG,
+    WRITE_CLIPBOARD_SOURCE_TAG,
+    READ_TEXT,
+    MAX_TRACKED_ACTION,
+  };
+
+  void ReportAction(Buffer buffer, TrackedAction action) const;
 #if defined(OS_WIN)
   void WriteBitmapFromHandle(HBITMAP source_hbitmap,
                              const gfx::Size& size);