Camera: Add exists function to CameraMetadata

Change-Id: I081f61417fca7c8408e9e767129647ddce5364ab
diff --git a/camera/CameraMetadata.cpp b/camera/CameraMetadata.cpp
index 0bfa420..fdd0610 100644
--- a/camera/CameraMetadata.cpp
+++ b/camera/CameraMetadata.cpp
@@ -208,6 +208,11 @@
     return res;
 }
 
+bool CameraMetadata::exists(uint32_t tag) const {
+    camera_metadata_ro_entry entry;
+    return find_camera_metadata_ro_entry(mBuffer, tag, &entry) == 0;
+}
+
 camera_metadata_entry_t CameraMetadata::find(uint32_t tag) {
     status_t res;
     camera_metadata_entry entry;