Write file:// tests for BufferedDataSource and fix some bugs as a result.

webkit/media/test_response_generator.cc

Index: webkit/media/test_response_generator.cc
diff --git a/webkit/media/test_response_generator.cc b/webkit/media/test_response_generator.cc
index d5485b38f83740260cb79d736b1eaa56484d805f..b2d605ca5967bdd163553f5c79a90a2f6632cc95 100644
--- a/webkit/media/test_response_generator.cc
+++ b/webkit/media/test_response_generator.cc
@@ -85,4 +85,17 @@ WebURLResponse TestResponseGenerator::Generate404() {
   return response;
 }
 
+WebURLResponse TestResponseGenerator::GenerateFileResponse(
+    int64 first_byte_offset) {
+  WebURLResponse response(gurl_);
+  response.setHTTPStatusCode(0);
+
+  if (first_byte_offset >= 0) {
+    response.setExpectedContentLength(content_length_ - first_byte_offset);
+  } else {
+    response.setExpectedContentLength(-1);
+  }
+  return response;
+}
+
 }  // namespace webkit_media