[fsp] Add support for providing thumbnails.

chrome/common/extensions/api/file_system_provider.idl

Index: chrome/common/extensions/api/file_system_provider.idl
diff --git a/chrome/common/extensions/api/file_system_provider.idl b/chrome/common/extensions/api/file_system_provider.idl
index 155c7da2d59b6bbaaa9293d75bb44c8c7af5c13d..75fd355a75f33c1fb358f522a3811378dfd0879c 100644
--- a/chrome/common/extensions/api/file_system_provider.idl
+++ b/chrome/common/extensions/api/file_system_provider.idl
@@ -49,7 +49,11 @@ namespace fileSystemProvider {
     [instanceOf=Date] object modificationTime;
 
     // Mime type for the entry.
-    DOMString? mimeType; 
+    DOMString? mimeType;
+
+    // Thumbnail image as a data URI. Optional, but can be provided only when

[hirono, 2014/08/27 09:20:07]

How about describing about image types of the thumbnail here?

[mtomasz, 2014/08/28 04:57:55]

Done.

+    // explicitely requested in the <code>onGetMetadataRequested</code> event.
+    DOMString? thumbnail;
   };
 
   // Represents a mounted file system.
@@ -82,6 +86,9 @@ namespace fileSystemProvider {
     DOMString fileSystemId;
     long requestId;
     DOMString entryPath;
+
+    // Set to <code>true</code> if the thumbnail is requested.
+    boolean thumbnail;
   };
 
   // Options for the <code>onReadDirectoryRequested()</code> event.