Remove Dezippering from OscillatorNode

Remove dezippering from the frequency and detune attributes. The values
are changed immediately instead of gradually changing from the old
value to the new.

Chromium Feature: https://www.chromestatus.com/features/5287995770929152
Intent to ship: https://groups.google.com/a/chromium.org/d/msg/blink-dev/YKYRrh0nWMo/aGzd3049AgAJ

Bug: 752987
Test: Oscillator/dezipper.html
Change-Id: I58df869ca99a24f6429c9cc50c1af2101dbdf03d
Reviewed-on: https://chromium-review.googlesource.com/609095
Commit-Queue: Raymond Toy <rtoy@chromium.org>
Reviewed-by: Hongchan Choi <hongchan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#532663}

third_party/WebKit/Source/modules/webaudio/OscillatorNode.cpp

@@ -184,10 +184,8 @@ bool OscillatorHandler::CalculateSampleAccuratePhaseIncrements(
     frequency_->CalculateSampleAccurateValues(phase_increments,
                                               frames_to_process);
   } else {
-    // Handle ordinary parameter smoothing/de-zippering if there are no
-    // scheduled changes.
-    frequency_->Smooth();
-    float frequency = frequency_->SmoothedValue();
+    // Handle ordinary parameter changes if there are no scheduled changes.
+    float frequency = frequency_->Value();
     final_scale *= frequency;
   }
 
@@ -212,10 +210,9 @@ bool OscillatorHandler::CalculateSampleAccuratePhaseIncrements(
            frames_to_process);
     }
   } else {
-    // Handle ordinary parameter smoothing/de-zippering if there are no
-    // scheduled changes.
-    detune_->Smooth();
-    float detune = detune_->SmoothedValue();
+    // Handle ordinary parameter changes if there are no scheduled
+    // changes.
+    float detune = detune_->Value();
     float detune_scale = powf(2, detune / 1200);
     final_scale *= detune_scale;
   }
@@ -393,8 +390,8 @@ void OscillatorHandler::Process(size_t frames_to_process) {
   float table_interpolation_factor = 0;
 
   if (!has_sample_accurate_values) {
-    frequency = frequency_->SmoothedValue();
-    float detune = detune_->SmoothedValue();
+    frequency = frequency_->Value();
+    float detune = detune_->Value();
     float detune_scale = powf(2, detune / 1200);
     frequency *= detune_scale;
     periodic_wave_->WaveDataForFundamentalFrequency(frequency, lower_wave_data,