ASSERT object is not nullptr in DeviceBase::ValidateObject

This patch adds an ASSERT expression on the object parameter of
DeviceBase::ValidateObject() so that Dawn won't crash in the debug
build when a nullptr object is being used unexpectedly.

BUG=dawn:209

Change-Id: I52ad57b58eb59edf04afc9963e260436d93e673e
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/12140
Reviewed-by: Corentin Wallez <cwallez@chromium.org>
Reviewed-by: Austin Eng <enga@chromium.org>
Commit-Queue: Jiawei Shao <jiawei.shao@intel.com>

src/dawn_native/Device.cpp

@@ -142,6 +142,7 @@ namespace dawn_native {
     }
 
     MaybeError DeviceBase::ValidateObject(const ObjectBase* object) const {
+        ASSERT(object != nullptr);
         if (DAWN_UNLIKELY(object->GetDevice() != this)) {
             return DAWN_VALIDATION_ERROR("Object from a different device.");
         }