gst_flow_data LLTng tracepoints.

The gst_flow_data tracepoints trace the properties of data flowing through the gstreamer pipeline.
They can be used to observe throughput of the pipeline and its elements.

The initial support for this kind of tracepoints includes calling appropriate primitives
when the data is passed through the pipeline elements:

1. At entry points of Push APIs:
    gst_pad_chain()
    gst_pad_chain_list()
    gst_pad_push()
    gst_pad_push_list()

2. At successful exit points of Pull APIs:
    gst_pad_get_range()
    gst_pad_pull_range()

The tracepoints are invoked just before the gst_flow tracepoints.

At this stage, only minimal data is stored for each tracepoint:

    -- a unique integer ID of the invoking thread;
    -- the value of the pointer to the data.
    -- the type of data: buffer or buffer list.

For buffer lists, every buffer in the list is also traced.

Signed-off-by: Alexander Barabash <alexander_barabash@mentor.com>
Support for gst_flow_event LLTng tracepoints.

The gst_flow_event tracepoints trace the properties of events sent through the gstreamer pipeline.
This replaces gst_flow_data tracepoints for event data.

The initial support for this kind of tracepoints includes calling appropriate primitives
when the data is passed through the pipeline elements, in the following APIs:

   gst_pad_push_event()
   gst_pad_send_event()

The tracepoints are invoked just before the gst_flow tracepoints.

At this stage, only minimal data is stored for each tracepoint:

    -- a unique integer ID of the invoking thread;
    -- the value of the pointer to the event.
    -- the type of event.

Signed-off-by: Alexander Barabash <alexander_barabash@mentor.com>
Added support for gst_flow_event_latency and gst_flow_event_qos LTTng tracepoints.

The gst_flow_event_latency tracepoints output the latency field of the GST_EVENT_LATENCY event.
This tracepoint immediately follows the gst_flow_event tracepoint and precedes
the gst_flow tracepoint on the same thread.

The gst_flow_event_qos tracepoints output the proportion and diff fields of the GST_EVENT_QOS event.
This tracepoint immediately follows the gst_flow_event tracepoint and precedes
the gst_flow tracepoint on the same thread.

Signed-off-by: Alexander Barabash <alexander_barabash@mentor.com>