Add histgrams to Folder shortcut feature in Files.app.

tools/metrics/histograms/histograms.xml

Index: tools/metrics/histograms/histograms.xml
diff --git a/tools/metrics/histograms/histograms.xml b/tools/metrics/histograms/histograms.xml
index f0c5161e109af3a2c12fd04d7c62fa465c97b961..ec1fe5684767d8799b373fc2c8d3b653d1e3faca 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -3885,6 +3885,31 @@ other types of suffix sets.
   </summary>
 </histogram>
 
+<histogram name="FileBrowser.FolderShortcut.Add">
+  <summary>
+    Chrome OS File Browser: this is recorded when the user adds a folder

[Alexei Svitkine (slow), 2013/08/12 17:22:47]

Nit: Don't we usually write ChromeOS in one word?

[yoshiki, 2013/08/12 22:28:00]

I think you're right. But in this file, "Chrome OS" is common. To make
consistency, "Chrome OS" is better in this case.

+    shortcut.
+  </summary>
+</histogram>
+
+<histogram name="FileBrowser.FolderShortcut.Count">
+  <summary>Chrome OS File Browser: number of folder shorcuts.</summary>

[Alexei Svitkine (slow), 2013/08/12 17:22:47]

Mention when this is recorded.

[yoshiki, 2013/08/12 22:28:00]

Added.

+</histogram>
+
+<histogram name="FileBrowser.FolderShortcut.Navigate">
+  <summary>
+    Chrome OS File Browser: this is recorded when the user clicks or selects a
+    folder shortcut and is navigated to the target folder.
+  </summary>
+</histogram>
+
+<histogram name="FileBrowser.FolderShortcut.Remove">
+  <summary>
+    Chrome OS File Browser: this is recorded when the user removes a folder
+    shortcut.
+  </summary>
+</histogram>
+
 <histogram name="FileBrowser.Load" units="milliseconds">
   <summary>
     Chrome OS File Browser is an built-in extension without a background page.