WebAudio: Fix OscillatorNode liveness

Canonical fix:
- Model liveness through OscillatorNode (AudioNode), i.e., keep alive
  listener from there.
- Change off-thread handler to use a weak root

This works as AudioNode disposes the handler in the pre-finalizer.

This fixes webaudio/Oscillator/osc-low-freq.html for unified heap
running with leak detection.

Bug: 928781, 843903
Change-Id: I58a76bb0d5a47e65e91516cde6c4fe77044cb8ae
Reviewed-on: https://chromium-review.googlesource.com/c/1488922
Commit-Queue: Michael Lippautz <mlippautz@chromium.org>
Reviewed-by: Kentaro Hara <haraken@chromium.org>
Reviewed-by: Hongchan Choi <hongchan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#635594}

third_party/blink/renderer/modules/webaudio/oscillator_node.cc

@@ -24,6 +24,7 @@
  */
 
 #include <algorithm>
+#include <limits>
 
 #include "third_party/blink/renderer/modules/webaudio/audio_node_output.h"
 #include "third_party/blink/renderer/modules/webaudio/oscillator_node.h"
@@ -525,7 +526,8 @@ OscillatorNode::OscillatorNode(BaseAudioContext& context,
                              AudioParamHandler::AutomationRate::kAudio,
                              AudioParamHandler::AutomationRateMode::kVariable,
                              -1200 * log2f(std::numeric_limits<float>::max()),
-                             1200 * log2f(std::numeric_limits<float>::max()))) {
+                             1200 * log2f(std::numeric_limits<float>::max()))),
+      periodic_wave_(wave_table) {
   SetHandler(OscillatorHandler::Create(
       *this, context.sampleRate(), oscillator_type, wave_table,
       frequency_->Handler(), detune_->Handler()));
@@ -568,6 +570,7 @@ OscillatorNode* OscillatorNode::Create(BaseAudioContext* context,
 void OscillatorNode::Trace(blink::Visitor* visitor) {
   visitor->Trace(frequency_);
   visitor->Trace(detune_);
+  visitor->Trace(periodic_wave_);
   AudioScheduledSourceNode::Trace(visitor);
 }
 
@@ -593,6 +596,7 @@ AudioParam* OscillatorNode::detune() {
 }
 
 void OscillatorNode::setPeriodicWave(PeriodicWave* wave) {
+  periodic_wave_ = wave;
   GetOscillatorHandler().SetPeriodicWave(wave);
 }
 

third_party/blink/renderer/modules/webaudio/oscillator_node.h

@@ -106,10 +106,8 @@ class OscillatorHandler final : public AudioScheduledSourceHandler {
   AudioFloatArray phase_increments_;
   AudioFloatArray detune_values_;
 
-  // This Persistent doesn't make a reference cycle including the owner
-  // OscillatorNode. It is cross-thread, as it will be accessed by the audio
-  // thread.
-  CrossThreadPersistent<PeriodicWave> periodic_wave_;
+  // PeriodicWave is held alive by OscillatorNode.
+  CrossThreadWeakPersistent<PeriodicWave> periodic_wave_;
 };
 
 class OscillatorNode final : public AudioScheduledSourceNode {
@@ -140,6 +138,9 @@ class OscillatorNode final : public AudioScheduledSourceNode {
  private:
   Member<AudioParam> frequency_;
   Member<AudioParam> detune_;
+  // This PeriodicWave is held alive here to allow referencing it from
+  // OscillatorHandler via weak reference.
+  Member<PeriodicWave> periodic_wave_;
 };
 
 }  // namespace blink