Store Layer ownerUid based on metadata or callingUid.

In most cases we want the Layer ownerUid to be the same as the
callingUid since the caller requesting to create the layer should be the
owner. However, in cases when the requst to create the layer comes from
a system process, we should attempt to use the UID passed into the
metadata. This is because the system process could request to create a
layer on behalf of another process.

Test: adb shell dumpsys SurfaceFlinger shows correct uid
Bug: 155825630
Change-Id: I633f293e087cdf413f7cb5e296bd923d83da841c