exponentialRampToValue doesn't use starting value

exponentialRampToValue doesn't use starting value
https://bugs.webkit.org/show_bug.cgi?id=78035

Patch by Raymond Toy <rtoy@google.com> on 2012-02-22
Reviewed by Chris Rogers.

Source/WebCore:

Test: webaudio/audioparam-exponentialRampToValueAtTime.html

* webaudio/AudioParamTimeline.cpp:
(WebCore::AudioParamTimeline::valuesForTimeRangeImpl): Set
starting value for exponential ramp.

LayoutTests:

* webaudio/audioparam-exponentialRampToValueAtTime-expected.txt: Added.
* webaudio/audioparam-exponentialRampToValueAtTime.html: Added.
* webaudio/resources/audioparam-testing.js: Added.
(createConstantBuffer):
(createExponentialRampArray):
(comparePartialSignals):
(verifyDiscontinuities):
(compareSignals):
(doAutomation):

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@108592 268f45cc-cd09-0410-ab3c-d52691b4dbfc