Convert frame count metadata key

AMEDIAFORMAT_KEY_FRAME_COUNT/kKeyFrameCount weren't being converted.

Bug: 119781577
Bug: 111407253
Test: CTS
Change-Id: I312cf8bac3b8471c0c2e10ff376ded7378086638
diff --git a/media/libstagefright/Utils.cpp b/media/libstagefright/Utils.cpp
index dd29474..4aee9d5 100644
--- a/media/libstagefright/Utils.cpp
+++ b/media/libstagefright/Utils.cpp
@@ -608,6 +608,7 @@
         { "temporal-layer-count", kKeyTemporalLayerCount },
         { "thumbnail-width", kKeyThumbnailWidth },
         { "thumbnail-height", kKeyThumbnailHeight },
+        { "frame-count", kKeyFrameCount },
     }
 };