Throw an error or return null if FlutterView.getBitmap fails (flutter…

…#5051)

getBitmap had been doing FXL_CHECK assertions to check memory allocation
failures and other errors.  getBitmap will now return null to the caller
instead.
(The VM may throw OutOfMemoryError or other exceptions if JNI APIs fail)

Fixes flutter/flutter#16750

shell/platform/android/platform_view_android_jni.cc

@@ -351,10 +351,14 @@ static jobject GetBitmap(JNIEnv* env, jobject jcaller, jlong shell_holder) {
   const SkISize& frame_size = screenshot.frame_size;
   jsize pixels_size = frame_size.width() * frame_size.height();
   jintArray pixels_array = env->NewIntArray(pixels_size);
-  FXL_CHECK(pixels_array);
+  if (pixels_array == nullptr) {
+    return nullptr;
+  }
 
   jint* pixels = env->GetIntArrayElements(pixels_array, nullptr);
-  FXL_CHECK(pixels);
+  if (pixels == nullptr) {
+    return nullptr;
+  }
 
   auto pixels_src = static_cast<const int32_t*>(screenshot.data->data());
 
@@ -371,27 +375,39 @@ static jobject GetBitmap(JNIEnv* env, jobject jcaller, jlong shell_holder) {
   env->ReleaseIntArrayElements(pixels_array, pixels, 0);
 
   jclass bitmap_class = env->FindClass("android/graphics/Bitmap");
-  FXL_CHECK(bitmap_class);
+  if (bitmap_class == nullptr) {
+    return nullptr;
+  }
 
   jmethodID create_bitmap = env->GetStaticMethodID(
       bitmap_class, "createBitmap",
       "([IIILandroid/graphics/Bitmap$Config;)Landroid/graphics/Bitmap;");
-  FXL_CHECK(create_bitmap);
+  if (create_bitmap == nullptr) {
+    return nullptr;
+  }
 
   jclass bitmap_config_class = env->FindClass("android/graphics/Bitmap$Config");
-  FXL_CHECK(bitmap_config_class);
+  if (bitmap_config_class == nullptr) {
+    return nullptr;
+  }
 
   jmethodID bitmap_config_value_of = env->GetStaticMethodID(
       bitmap_config_class, "valueOf",
       "(Ljava/lang/String;)Landroid/graphics/Bitmap$Config;");
-  FXL_CHECK(bitmap_config_value_of);
+  if (bitmap_config_value_of == nullptr) {
+    return nullptr;
+  }
 
   jstring argb = env->NewStringUTF("ARGB_8888");
-  FXL_CHECK(argb);
+  if (argb == nullptr) {
+    return nullptr;
+  }
 
   jobject bitmap_config = env->CallStaticObjectMethod(
       bitmap_config_class, bitmap_config_value_of, argb);
-  FXL_CHECK(bitmap_config);
+  if (bitmap_config == nullptr) {
+    return nullptr;
+  }
 
   return env->CallStaticObjectMethod(bitmap_class, create_bitmap, pixels_array,
                                      frame_size.width(), frame_size.height(),