Convert AudioBufferSource start and loop-comprehensive tests to testharness

third_party/WebKit/LayoutTests/webaudio/AudioBufferSource/audiobuffersource-start-expected.txt

-Tests AudioBufferSourceNode start() with a variety of offsets and durations.
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-On success, you will see a series of "PASS" messages, followed by "TEST COMPLETE".
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-PASS  start(when): implicitly play whole buffer from beginning to end.
-PASS  start(when, 0): play whole buffer from beginning to end explicitly giving offset of 0.
-PASS  start(when, 0, 8_frames): play whole buffer from beginning to end explicitly giving offset of 0 and duration of 8 frames.
-PASS  start(when, 4_frames): play with explicit non-zero offset.
-PASS  start(when, 4_frames, 4_frames): play with explicit non-zero offset and duration.
-PASS  start(when, 7_frames): play with explicit non-zero offset near end of buffer.
-PASS  start(when, 8_frames): play with explicit offset at end of buffer.
-PASS  start(when, 9_frames): play with explicit offset past end of buffer.
-PASS  start(when, 0, 15_frames): play with whole buffer, with long duration (clipped).
-PASS successfullyParsed is true
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-TEST COMPLETE
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