Implement WebM subsample support

media/formats/webm/webm_crypto_helpers.h

Index: media/formats/webm/webm_crypto_helpers.h
diff --git a/media/formats/webm/webm_crypto_helpers.h b/media/formats/webm/webm_crypto_helpers.h
index 041fb2b8020abdeb32725504e014fa13c215e679..21e53f7409ddf932fea6123169cd4ecca8285bf1 100644
--- a/media/formats/webm/webm_crypto_helpers.h
+++ b/media/formats/webm/webm_crypto_helpers.h
@@ -10,6 +10,7 @@
 #include <memory>
 
 #include "media/base/decoder_buffer.h"
+#include "media/base/media_export.h"
 
 namespace media {
 
@@ -20,12 +21,13 @@ namespace media {
 // false otherwise, in which case |decrypt_config| and |data_offset| will not be
 // changed. Current encrypted WebM request for comments specification is here
 // http://wiki.webmproject.org/encryption/webm-encryption-rfc
-bool WebMCreateDecryptConfig(const uint8_t* data,
-                             int data_size,
-                             const uint8_t* key_id,
-                             int key_id_size,
-                             std::unique_ptr<DecryptConfig>* decrypt_config,
-                             int* data_offset);
+bool MEDIA_EXPORT
+WebMCreateDecryptConfig(const uint8_t* data,
+                        int data_size,
+                        const uint8_t* key_id,
+                        int key_id_size,
+                        std::unique_ptr<DecryptConfig>* decrypt_config,
+                        int* data_offset);
 
 }  // namespace media