[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..bbc6bc626483584c57c30f5317719eacd59ae40c 100644
--- a/chrome/common/extensions/api/file_system_provider.idl
+++ b/chrome/common/extensions/api/file_system_provider.idl
@@ -49,7 +49,12 @@ namespace fileSystemProvider {
     [instanceOf=Date] object modificationTime;
 
     // Mime type for the entry.
-    DOMString? mimeType; 
+    DOMString? mimeType;
+
+    // Thumbnail image as a data URI in either PNG, JPEG or WEBP format, at most
+    // 32 KB in size. Optional, but can be provided only when explicitly
+    // requested by the <code>onGetMetadataRequested</code> event.
+    DOMString? thumbnail;
   };
 
   // Represents a mounted file system.
@@ -82,6 +87,9 @@ 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.