Webview: Release MediaMetadataRetriever after getting media info

- MediaResourceGetter creates a MediaMetadataRetriever object
  in order to get clip duration, width, and height.
- After getting the required info, the object should be released.
- MediaMetadataRetriever creates a connection that requires this
  data continuously in the background, particularly in streaming
  use-cases.

Change-Id: I20dc9f4ca7c38fe7968c78c5b8e2274d6864579d
1 file changed