CCA: Disable echo cancellation when recording

Echo cancellation is mainly for video conferencing. Disable it in CCA
could save ~10% cpu on Nocturne in video recording.

Bug: b:139788862
Test: Record video on Nocturne, measure performance by pprof and top.

Change-Id: Ib531c338a46e9a6c611e269ade1e96541be764ab
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1864757Reviewed-by: Wei Lee <wtlee@chromium.org>
Commit-Queue: Shik Chen <shik@chromium.org>
Cr-Commit-Position: refs/heads/master@{#706406}

chrome/browser/resources/chromeos/camera/src/js/device/constraints_preferrer.js

@@ -326,7 +326,7 @@ cca.device.VideoConstraintsPreferrer =
     };
 
     const toConstraints = (width, height, fps) => ({
-      audio: true,
+      audio: {echoCancellation: false},
       video: {
         deviceId: {exact: deviceId},
         frameRate: fps ? {exact: fps} : {min: 24},

chrome/browser/resources/chromeos/camera/src/js/views/camera/modes.js

@@ -254,7 +254,10 @@ cca.views.camera.Modes.getV1Constraints = async function(videoMode, deviceId) {
       // deviceId is set to null for requesting camera with default facing.
       constraint.facingMode = {exact: defaultFacing};
     }
-    return {audio: videoMode, video: constraint};
+    return {
+      audio: videoMode ? {echoCancellation: false} : false,
+      video: constraint,
+    };
   });
 };