Pass through slow-motion metadata buffer

bug: 160260201
test: manually verify that a hard-coded slow-motion data buffer is
passed through from plugin to MediaExtractor api level.

Change-Id: I27f18d58b385194c5fc682c1d3947e9916e77f9e
diff --git a/media/ndk/NdkMediaFormat.cpp b/media/ndk/NdkMediaFormat.cpp
index 8680641..73c52a9 100644
--- a/media/ndk/NdkMediaFormat.cpp
+++ b/media/ndk/NdkMediaFormat.cpp
@@ -364,6 +364,7 @@
 EXPORT const char* AMEDIAFORMAT_KEY_SAR_WIDTH = "sar-width";
 EXPORT const char* AMEDIAFORMAT_KEY_SEI = "sei";
 EXPORT const char* AMEDIAFORMAT_KEY_SLICE_HEIGHT = "slice-height";
+EXPORT const char* AMEDIAFORMAT_KEY_SLOW_MOTION_MARKERS = "slow-motion-markers";
 EXPORT const char* AMEDIAFORMAT_KEY_STRIDE = "stride";
 EXPORT const char* AMEDIAFORMAT_KEY_TARGET_TIME = "target-time";
 EXPORT const char* AMEDIAFORMAT_KEY_TEMPORAL_LAYER_COUNT = "temporal-layer-count";