multipaste: Update enum for CH display format

Update the enum 3 to have a human readable label.

Bug: 1164526
Change-Id: Ic716ceff4128c4778f61e98eb70d46d837288bf7
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2643414
Auto-Submit: Alex Newcomer <newcomer@chromium.org>
Reviewed-by: Andrew Xu <andrewxu@chromium.org>
Commit-Queue: Alex Newcomer <newcomer@chromium.org>
Cr-Commit-Position: refs/heads/master@{#845915}

ash/clipboard/clipboard_history_util.h

@@ -60,8 +60,9 @@ enum ClipboardHistoryMenuViewID {
 };
 
 // Used in histograms, each value corresponds with an underlying format
-// displayed by a ClipboardHistoryItemView. Do not reorder entries, if you must
-// add to it, add at the end.
+// displayed by a ClipboardHistoryItemView, shown as
+// ClipboardHistoryDisplayFormat in enums.xml. Do not reorder entries, if you
+// must add to it, add at the end.
 enum class ClipboardHistoryDisplayFormat {
   kText = 0,
   kBitmap = 1,

tools/metrics/histograms/enums.xml

@@ -11514,6 +11514,7 @@ histogram as enum -->
   <int value="0" label="Text"/>
   <int value="1" label="Bitmap"/>
   <int value="2" label="Html"/>
+  <int value="3" label="File"/>
 </enum>
 
 <enum name="ClipboardHistoryPlaceholderStringType">