[fsp] Add support for truncating files.

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 7bd3a8255798149c7a2b7482d0b37d3208898a5b..66114eaf0b0fe21015fd620ab443b80e658332f0 100644
--- a/chrome/common/extensions/api/file_system_provider.idl
+++ b/chrome/common/extensions/api/file_system_provider.idl
@@ -149,6 +149,14 @@ namespace fileSystemProvider {
     DOMString targetPath;
   };
 
+  // Options for the <code>onTruncateRequested()</code> event.
+  dictionary TruncateRequestedOptions {
+    DOMString fileSystemId;
+    long requestId;
+    DOMString filePath;
+    double length;
+  };
+
   // Callback to receive the result of mount() function.
   callback MountCallback = void([nodoc, instanceOf=DOMError] object error);
 
@@ -296,6 +304,13 @@ namespace fileSystemProvider {
         MoveEntryRequestedOptions options,
         ProviderSuccessCallback successCallback,
         ProviderErrorCallback errorCallback);
+
+    // Raised when truncating a file to a desired length is requested.
+    // If an error occurs, then <code>errorCallback</code> must be called.
+    [maxListeners=1, nodoc] static void onTruncateRequested(
+        TruncateRequestedOptions options,
+        ProviderSuccessCallback successCallback,
+        ProviderErrorCallback errorCallback);
   };
 };