Protect AudioScheduledSoureNode::m_startTime and m_endTime.

Source/modules/webaudio/OscillatorNode.h

Index: Source/modules/webaudio/OscillatorNode.h
diff --git a/Source/modules/webaudio/OscillatorNode.h b/Source/modules/webaudio/OscillatorNode.h
index 66a0497daffb30cbf8b6f688fba217adc2db3daf..d80f27dc84e8bbc7409c4146d7e1d00cbe016600 100644
--- a/Source/modules/webaudio/OscillatorNode.h
+++ b/Source/modules/webaudio/OscillatorNode.h
@@ -88,9 +88,6 @@ private:
     // Since it's floating-point, it has sub-sample accuracy.
     double m_virtualReadIndex;
 
-    // This synchronizes process().
-    mutable Mutex m_processLock;
-
     // Stores sample-accurate values calculated according to frequency and detune.
     AudioFloatArray m_phaseIncrements;
     AudioFloatArray m_detuneValues;