Implement Encoding API

LayoutTests/fast/encoding/api/basics-expected.txt

+This tests the basics of the Encoding API.
+
+On success, you will see a series of "PASS" messages, followed by "TEST COMPLETE".
+
+
+PASS 'TextEncoder' in window is true
+PASS 'TextDecoder' in window is true
+PASS 'encoding' in new TextEncoder is true
+PASS 'encoding' in new TextDecoder is true
+PASS typeof (new TextEncoder).encoding is "string"
+PASS typeof (new TextDecoder).encoding is "string"
+PASS 'encode' in new TextEncoder is true
+PASS 'decode' in new TextDecoder is true
+PASS typeof (new TextEncoder).encode is "function"
+PASS typeof (new TextDecoder).decode is "function"
+PASS (new TextEncoder).encoding is "utf-8"
+PASS (new TextDecoder).encoding is "utf-8"
+
+test encode/decode sample - utf-8
+encoded = new TextEncoder('utf-8').encode("z¢水𝄞􏿽")
+PASS JSON.stringify(toArray(encoded)) is "[122,194,162,230,176,180,240,157,132,158,244,143,191,189]"
+PASS new TextDecoder('utf-8').decode(new Uint8Array([122,194,162,230,176,180,240,157,132,158,244,143,191,189])) is "z¢水𝄞􏿽"
+
+test encode/decode sample - utf-16le
+encoded = new TextEncoder('utf-16le').encode("z¢水𝄞􏿽")
+PASS JSON.stringify(toArray(encoded)) is "[122,0,162,0,52,108,52,216,30,221,255,219,253,223]"
+PASS new TextDecoder('utf-16le').decode(new Uint8Array([122,0,162,0,52,108,52,216,30,221,255,219,253,223])) is "z¢水𝄞􏿽"
+
+test encode/decode sample - utf-16be
+encoded = new TextEncoder('utf-16be').encode("z¢水𝄞􏿽")
+PASS JSON.stringify(toArray(encoded)) is "[0,122,0,162,108,52,216,52,221,30,219,255,223,253]"
+PASS new TextDecoder('utf-16be').decode(new Uint8Array([0,122,0,162,108,52,216,52,221,30,219,255,223,253])) is "z¢水𝄞􏿽"
+
+test encode/decode sample - utf-16
+encoded = new TextEncoder('utf-16').encode("z¢水𝄞􏿽")
+PASS JSON.stringify(toArray(encoded)) is "[122,0,162,0,52,108,52,216,30,221,255,219,253,223]"
+PASS new TextDecoder('utf-16').decode(new Uint8Array([122,0,162,0,52,108,52,216,30,221,255,219,253,223])) is "z¢水𝄞􏿽"
+PASS successfullyParsed is true
+
+TEST COMPLETE
+