android: add static, default model for gltf-viewer (#8898)

The default gltf for android's gltf-viewer is the buster drone,
which uses skinning.

We add an additional model (damaged helmet) as an alternative
default. This will be useful for debugging WebGPU, where skinnning is
not yet supported. This alternate path can only be invoke by starting
the app through adb:

  `adb shell am start -n com.google.android.filament.gltf/.MainActivity --ez "use-static-model" true`

android/samples/sample-gltf-viewer/src/main/java/com/google/android/filament/gltf/MainActivity.kt

@@ -18,6 +18,7 @@ package com.google.android.filament.gltf
 
 import android.annotation.SuppressLint
 import android.app.Activity
+import android.content.Intent
 import android.os.Bundle
 import android.util.Log
 import android.view.*
@@ -50,6 +51,7 @@ class MainActivity : Activity() {
         // Load the library for the utility layer, which in turn loads gltfio and the Filament core.
         init { Utils.init() }
         private const val TAG = "gltf-viewer"
+        private const val STATIC_MODEL_TAG = "use-static-model"
     }
 
     private lateinit var surfaceView: SurfaceView
@@ -69,6 +71,7 @@ class MainActivity : Activity() {
     private var loadStartTime = 0L
     private var loadStartFence: Fence? = null
     private val viewerContent = AutomationEngine.ViewerContent()
+    private var useStaticModel = false
 
     @SuppressLint("ClickableViewAccessibility")
     override fun onCreate(savedInstanceState: Bundle?) {
@@ -83,6 +86,12 @@ class MainActivity : Activity() {
         doubleTapDetector = GestureDetector(applicationContext, doubleTapListener)
         singleTapDetector = GestureDetector(applicationContext, singleTapListener)
 
+        val intent: Intent = intent
+        val bundle: Bundle? = intent.extras
+        bundle?.let {
+            useStaticModel = it.getBoolean(STATIC_MODEL_TAG, false)
+        }
+
         modelViewer = ModelViewer(surfaceView)
         viewerContent.view = modelViewer.view
         viewerContent.sunlight = modelViewer.light
@@ -141,7 +150,16 @@ class MainActivity : Activity() {
     }
 
     private fun createDefaultRenderables() {
-        val buffer = assets.open("models/scene.gltf").use { input ->
+        // Sometimes it's useful to set to the default model to something static. You can enable
+        // the static model by launching the app from adb, as in
+        // `adb shell am start -n com.google.android.filament.gltf/.MainActivity --ez "use-static-model" true`
+        val modelPath = if (useStaticModel) {
+            "models/helmet.glb"
+        } else {
+            "models/scene.gltf"
+        }
+
+        val buffer = assets.open(modelPath).use { input ->
             val bytes = ByteArray(input.available())
             input.read(bytes)
             ByteBuffer.wrap(bytes)