Move MediaStream and MediaStreamTrack implementation from modules/mediastream to core/mediastream.

LayoutTests/fast/mediastream/RTCPeerConnection-datachannel-expected.txt

-Tests RTCDataChannel.
-
-On success, you will see a series of "PASS" messages, followed by "TEST COMPLETE".
-
-
-PASS dc = pc.createDataChannel("label1"); did not throw exception.
-PASS dc.reliable is true
-PASS dc = pc.createDataChannel("label2", {}); did not throw exception.
-PASS dc.reliable is true
-PASS dc = pc.createDataChannel("label3", {ordered:true}); did not throw exception.
-PASS dc.reliable is true
-PASS dc = pc.createDataChannel("label3", {ordered:false}); did not throw exception.
-PASS dc.reliable is false
-PASS dc = pc.createDataChannel("label3", {maxRetransmits:0}); did not throw exception.
-PASS dc.reliable is false
-PASS dc = pc.createDataChannel("label3", {maxRetransmitTime:0}); did not throw exception.
-PASS dc.reliable is false
-PASS pc is connected
-PASS dc = pc.createDataChannel("label"); did not throw exception.
-PASS dc.readyState is 'connecting'
-PASS pc_ondatachannel was called
-PASS dc_onopen was called
-PASS dc.readyState is 'open'
-PASS dc.label is 'label'
-PASS dc.send('xyzzy'); did not throw exception.
-PASS dc_onmessage_string was called
-PASS data is 'xyzzy'
-PASS dc.send(buffer); did not throw exception.
-PASS dc_onmessage_arraybuffer was called
-PASS data.byteLength is 2
-PASS array[0] is 17
-PASS array[1] is 19
-PASS data.byteLength is 12
-PASS dc.send(shrunkView); did not throw exception.
-PASS dc_onmessage_dataview was called
-PASS data.byteLength is 10
-PASS array[0] is 1
-PASS array[9] is 10
-PASS dc_onclose was called
-PASS dc.readyState is 'closed'
-PASS successfullyParsed is true
-
-TEST COMPLETE
-