[fsp] Add support for providing thumbnails.

chrome/renderer/resources/extensions/file_system_provider_custom_bindings.js

Index: chrome/renderer/resources/extensions/file_system_provider_custom_bindings.js
diff --git a/chrome/renderer/resources/extensions/file_system_provider_custom_bindings.js b/chrome/renderer/resources/extensions/file_system_provider_custom_bindings.js
index 020c772c849df1e94f07bcba46aad5888b11fd50..cbf3397e70d5cf93ecb004d4d64f63e81aabeb20 100644
--- a/chrome/renderer/resources/extensions/file_system_provider_custom_bindings.js
+++ b/chrome/renderer/resources/extensions/file_system_provider_custom_bindings.js
@@ -38,6 +38,8 @@ function annotateMetadata(metadata) {
   };
   if ('mimeType' in metadata)
     result.mimeType = metadata.mimeType;
+  if ('thumbnail' in metadata)
+    result.thumbnail = metadata.thumbnail;
   return result;
 }
 
@@ -141,6 +143,16 @@ eventBindings.registerArgumentMassager(
       var executionStart = Date.now();
       var options = args[0];
       var onSuccessCallback = function(metadata) {
+        // It is invalid to return a thumbnail when it's not requested. The
+        // restriction is added in order to avoid fetching the thumbnail while
+        // it's not needed.
+        if (!options.thumbnail && metadata.thumbnail) {

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

How about checking format of thumbnail?
The string may not start with 'data:' and valid image types.

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

Good idea. If users passed something invalid (like http://... for urls allowed
by our csp) then it could affect security. Added here and a sanity check in
get_metadata.cc. Done.

+          fileSystemProviderInternal.operationRequestedError(
+              options.fileSystemId, options.requestId, 'FAILED',
+              Date.now() - executionStart);
+          throw new Error('Thumbnail data is provided, but not requested.');
+        }
+
         fileSystemProviderInternal.getMetadataRequestedSuccess(
             options.fileSystemId,
             options.requestId,
@@ -162,6 +174,16 @@ eventBindings.registerArgumentMassager(
       var options = args[0];
       var onSuccessCallback = function(entries, hasNext) {
         var annotatedEntries = entries.map(annotateMetadata);
+        // It is invalid to return a thumbnail when it's not requested.
+        annotatedEntries.forEach(function(metadata) {
+          if (metadata.thumbnail) {
+            fileSystemProviderInternal.operationRequestedError(
+                options.fileSystemId, options.requestId, 'FAILED',
+                Date.now() - executionStart);
+            throw new Error(
+                'Thumbnails must not be provided when reading a directory.');
+          }
+        });
         fileSystemProviderInternal.readDirectoryRequestedSuccess(
             options.fileSystemId, options.requestId, annotatedEntries, hasNext,
             Date.now() - executionStart);