Move out expiry date by 6 months for expiring WebAudio histograms

Extend expiration by 6 months for WebAudio histograms expiring on 2021-01-06.

Bug: 1152046, 1152047, 1152048, 1152049, 1152050, 1152051, 1152052
Change-Id: I62f01eadf5bc891c5b4de3039c0ce80f2b3a0557
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2577878Reviewed-by: Hongchan Choi <hongchan@chromium.org>
Reviewed-by: Weilun Shi <sweilun@chromium.org>
Reviewed-by: Ilya Sherman <isherman@chromium.org>
Commit-Queue: Raymond Toy <rtoy@chromium.org>
Cr-Commit-Position: refs/heads/master@{#835324}

tools/metrics/histograms/histograms_xml/web_audio/histograms.xml

@@ -32,7 +32,7 @@ reviews. Googlers can read more about this at go/gwsq-gerrit.
 </histogram>
 
 <histogram name="WebAudio.AudioBuffer.NumberOfChannels" units="units"
-    expires_after="2021-01-06">
+    expires_after="2021-07-06">
   <owner>rtoy@chromium.org</owner>
   <owner>hongchan@chromium.org</owner>
   <summary>
@@ -52,7 +52,7 @@ reviews. Googlers can read more about this at go/gwsq-gerrit.
 </histogram>
 
 <histogram name="WebAudio.AudioBuffer.SampleRateRatio384kHz" units="units"
-    expires_after="2021-01-06">
+    expires_after="2021-07-06">
   <owner>rtoy@chromium.org</owner>
   <owner>hongchan@chromium.org</owner>
   <summary>
@@ -73,7 +73,7 @@ reviews. Googlers can read more about this at go/gwsq-gerrit.
 </histogram>
 
 <histogram name="WebAudio.AudioContext.MaxChannelsAvailable" units="units"
-    expires_after="2021-01-06">
+    expires_after="2021-07-06">
   <owner>rtoy@chromium.org</owner>
   <owner>hongchan@chromium.org</owner>
   <summary>
@@ -165,7 +165,7 @@ reviews. Googlers can read more about this at go/gwsq-gerrit.
 </histogram>
 
 <histogram name="WebAudio.BiquadFilter.Type" enum="BiquadFilterType"
-    expires_after="2021-01-06">
+    expires_after="2021-07-06">
   <owner>rtoy@chromium.org</owner>
   <owner>hongchan@chromium.org</owner>
   <summary>
@@ -187,7 +187,7 @@ reviews. Googlers can read more about this at go/gwsq-gerrit.
 </histogram>
 
 <histogram name="WebAudio.IIRFilterNode.Order" units="units"
-    expires_after="2021-01-06">
+    expires_after="2021-07-06">
   <owner>rtoy@chromium.org</owner>
   <owner>hongchan@chromium.org</owner>
   <summary>
@@ -198,7 +198,7 @@ reviews. Googlers can read more about this at go/gwsq-gerrit.
 </histogram>
 
 <histogram name="WebAudio.OfflineAudioContext.ChannelCount" units="units"
-    expires_after="2021-01-06">
+    expires_after="2021-07-06">
   <owner>rtoy@chromium.org</owner>
   <owner>hongchan@chromium.org</owner>
   <summary>
@@ -231,7 +231,7 @@ reviews. Googlers can read more about this at go/gwsq-gerrit.
 </histogram>
 
 <histogram name="WebAudio.PannerNode.PanningModel" enum="PanningModelType"
-    expires_after="2021-01-06">
+    expires_after="2021-07-06">
   <owner>rtoy@chromium.org</owner>
   <owner>hongchan@chromium.org</owner>
   <summary>
@@ -244,7 +244,7 @@ reviews. Googlers can read more about this at go/gwsq-gerrit.
 </histogram>
 
 <histogram name="WebAudio.PushPullFIFO.UnderflowGlitches" enum="Boolean"
-    expires_after="2021-01-06">
+    expires_after="2021-07-06">
   <owner>rtoy@chromium.org</owner>
   <owner>hongchan@chromium.org</owner>
   <summary>
@@ -255,7 +255,7 @@ reviews. Googlers can read more about this at go/gwsq-gerrit.
 </histogram>
 
 <histogram name="WebAudio.PushPullFIFO.UnderflowPercentage" units="%"
-    expires_after="2021-01-06">
+    expires_after="2021-07-06">
   <owner>rtoy@chromium.org</owner>
   <owner>hongchan@chromium.org</owner>
   <summary>