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

webkit/media/test_response_generator.h

Index: webkit/media/test_response_generator.h
diff --git a/webkit/media/test_response_generator.h b/webkit/media/test_response_generator.h
index d912d88715f54004712b7c6dd8a40cb478a9895f..f73e94bcb81fc0b0b04d7d74164226add15ed5cd 100644
--- a/webkit/media/test_response_generator.h
+++ b/webkit/media/test_response_generator.h
@@ -45,6 +45,13 @@ class TestResponseGenerator {
   // Generates a regular HTTP 404 response.
   WebKit::WebURLResponse Generate404();
 
+  // Generates a file:// response starting from |first_byte_offset| until the
+  // end of the resource.
+  //
+  // If |first_byte_offset| is negative a response containing no content length
+  // will be returned.
+  WebKit::WebURLResponse GenerateFileResponse(int64 first_byte_offset);
+
   const GURL& gurl() { return gurl_; }
   int64 content_length() { return content_length_; }