Webview: Release MediaMetadataRetriever after get media info

- MediaResourceGetter create an object of MediaMetadataRetriever,
  in order to get the duration, width, height of the clip.
- After got enough info, the object should be released.
- Especially in streaming, MediaMetadataRetriever will create a
  connection which will require the data continuously in
  background.

Change-Id: I20dc9f4ca7c38fe7968c78c5b8e2274d6864579d
Webview: Implement the suspend/resume operation in webview of chromium

- To use the new APIs (suspend/resume) of MediaPlayer
- Suspend will release the decoders and maintain the cached data for
  http streaming, instead of release the whole player.
- Resume will init the decoders before start() is called.

Change-Id: Iab7a7c8abb00368cb1eb15ba267f92689cc50be3