CdmFileIOImpl: Always SetLength(0) before WriteFile().

media/cdm/ppapi/cdm_file_io_impl.cc

Index: media/cdm/ppapi/cdm_file_io_impl.cc
diff --git a/media/cdm/ppapi/cdm_file_io_impl.cc b/media/cdm/ppapi/cdm_file_io_impl.cc
index 726388949ec483ef1ad05191e95a212b0677d29f..4dd13bfaa5e3d7e54b631ab1317f35cc9bde8e27 100644
--- a/media/cdm/ppapi/cdm_file_io_impl.cc
+++ b/media/cdm/ppapi/cdm_file_io_impl.cc
@@ -166,7 +166,12 @@ void CdmFileIOImpl::Write(const uint8_t* data, uint32_t data_size) {
   state_ = WRITING_FILE;
 
   // Always SetLength() in case |data_size| is less than the file size.
-  SetLength(data_size);
+  // Otherwise only part of the file is overwritten and the file length will
+  // remain the old length.
+  // Set length to 0 instead of |data_size| to avoid a corrupted file if
+  // |this| is destructed after SetLength() is called but before WriteFile()
+  // is called.
+  SetLength(0);
 }
 
 void CdmFileIOImpl::Close() {