Treat frustum changes as camera changes in Scene#render

Before this change, the user could update the frustum but not the camera
by resizing the viewer. The Scene would continue to render even when
requestRenderMode was enabled because it recognized the frustum had
changed, but would not update the cached camera to mark the change as
handled. This commit changes cameraEqual (in Scene.js) to take into
account the camera frustum.

Fixes CesiumGS#6812

Author: Luke San Antonio Bialecki

Source/Scene/Scene.js

@@ -1488,7 +1488,8 @@ define([
                Cartesian3.equalsEpsilon(camera0.direction, camera1.direction, epsilon) &&
                Cartesian3.equalsEpsilon(camera0.up, camera1.up, epsilon) &&
                Cartesian3.equalsEpsilon(camera0.right, camera1.right, epsilon) &&
-               Matrix4.equalsEpsilon(camera0.transform, camera1.transform, epsilon);
+               Matrix4.equalsEpsilon(camera0.transform, camera1.transform, epsilon) &&
+               camera0.frustum.equalsEpsilon(camera1.frustum, epsilon);
     }
 
     function updateDerivedCommands(scene, command) {
@@ -3172,13 +3173,17 @@ define([
 
     function checkForCameraUpdates(scene) {
         var camera = scene._camera;
-        if (!cameraEqual(camera, scene._cameraClone, CesiumMath.EPSILON15)) {
+        var cameraClone = scene._cameraClone;
+
+        scene._frustumChanged = !camera.frustum.equals(cameraClone.frustum);
+
+        if (!cameraEqual(camera, cameraClone, CesiumMath.EPSILON15)) {
             if (!scene._cameraStartFired) {
                 camera.moveStart.raiseEvent();
                 scene._cameraStartFired = true;
             }
             scene._cameraMovedTime = getTimestamp();
-            Camera.clone(camera, scene._cameraClone);
+            Camera.clone(camera, cameraClone);
 
             return true;
         }
@@ -3310,10 +3315,8 @@ define([
         tryAndCatchError(this, time, update);
         this._postUpdate.raiseEvent(this, time);
 
-        this._frustumChanged = !this._camera.frustum.equals(this._cameraClone.frustum);
-
         var cameraChanged = checkForCameraUpdates(this);
-        var shouldRender = !this.requestRenderMode || this._renderRequested || cameraChanged || this._frustumChanged || this._logDepthBufferDirty || (this.mode === SceneMode.MORPHING);
+        var shouldRender = !this.requestRenderMode || this._renderRequested || cameraChanged || this._logDepthBufferDirty || (this.mode === SceneMode.MORPHING);
         if (!shouldRender && defined(this.maximumRenderTimeChange) && defined(this._lastRenderTime)) {
             var difference = Math.abs(JulianDate.secondsDifference(this._lastRenderTime, time));
             shouldRender = shouldRender || difference > this.maximumRenderTimeChange;