Implement suspend() and resume() for OfflineAudioContext

LayoutTests/webaudio/offlineaudiocontext-suspend-resume-eventhandler-expected.txt

+CONSOLE ERROR: line 37: Uncaught (in promise) InvalidStateError: cannot schedule a suspend in the past, beyond the total render duration or at the duplicate position.
+Test event handler callback from OfflineAudioContext resume/suspend.
+
+On success, you will see a series of "PASS" messages, followed by "TEST COMPLETE".
+
+
+PASS context.currentTime is equal to 0.09868480725623582.

[Raymond Toy, 2015/05/28 16:37:34]

Might be nice to include the render quantum index to we can see this is
incrementing in nice way.

[hongchan, 2015/06/09 20:49:58]

Should we check if those indices match with the computed ones? I think it is a
bit excessive. Also not sure how to print out additional information as a result
while not doing pass/fail check.

+PASS context.currentTime is equal to 0.19736961451247165.
+PASS context.currentTime is equal to 0.2960544217687075.
+PASS context.currentTime is equal to 0.3947392290249433.
+PASS context.currentTime is equal to 0.49342403628117915.
+PASS context.currentTime is equal to 0.592108843537415.
+PASS context.currentTime is equal to 0.6907936507936508.
+PASS context.currentTime is equal to 0.7894784580498866.
+PASS context.currentTime is equal to 0.8881632653061224.
+PASS context.currentTime is equal to 0.9868480725623583.
+PASS context.currentTime is equal to 1.0855328798185941.
+PASS context.currentTime is equal to 1.18421768707483.
+PASS context.currentTime is equal to 1.2829024943310658.
+PASS context.currentTime is equal to 1.3815873015873017.
+PASS context.currentTime is equal to 1.4802721088435373.
+PASS context.currentTime is equal to 1.5789569160997732.
+PASS context.currentTime is equal to 1.677641723356009.
+PASS context.currentTime is equal to 1.7763265306122449.
+PASS context.currentTime is equal to 1.8750113378684807.
+PASS context.currentTime is equal to 1.9736961451247166.
+PASS context.state is equal to closed.
+PASS successfullyParsed is true
+
+TEST COMPLETE
+