[Autofill Assistant] Fixed animations when changing generic UI root view

Before this change, going from one ShowGenericUiAction to another one
caused a hard layout transition, rather than a smooth one.

Bug: b/145043394
Change-Id: I2577c03d9f9c8ebcb9d7f27cb057384f53a3edff
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2151452Reviewed-by: Marian Fechete <marianfe@google.com>
Commit-Queue: Clemens Arbesser <arbesser@google.com>
Cr-Commit-Position: refs/heads/master@{#759668}

chrome/android/features/autofill_assistant/java/src/org/chromium/chrome/browser/autofill_assistant/AssistantBottomBarCoordinator.java

@@ -25,6 +25,7 @@ import org.chromium.chrome.browser.autofill_assistant.details.AssistantDetailsCo
 import org.chromium.chrome.browser.autofill_assistant.form.AssistantFormCoordinator;
 import org.chromium.chrome.browser.autofill_assistant.form.AssistantFormModel;
 import org.chromium.chrome.browser.autofill_assistant.generic_ui.AssistantGenericUiCoordinator;
+import org.chromium.chrome.browser.autofill_assistant.generic_ui.AssistantGenericUiModel;
 import org.chromium.chrome.browser.autofill_assistant.header.AssistantHeaderCoordinator;
 import org.chromium.chrome.browser.autofill_assistant.header.AssistantHeaderModel;
 import org.chromium.chrome.browser.autofill_assistant.infobox.AssistantInfoBoxCoordinator;
@@ -248,6 +249,12 @@ class AssistantBottomBarCoordinator implements AssistantPeekHeightCoordinator.De
                 animateChildren(rootView);
             }
         });
+
+        model.getGenericUiModel().addObserver((source, propertyKey) -> {
+            if (AssistantGenericUiModel.VIEW == propertyKey) {
+                animateChildren(rootView);
+            }
+        });
     }
 
     private void animateChildren(ViewGroup rootView) {

chrome/android/features/autofill_assistant/java/src/org/chromium/chrome/browser/autofill_assistant/generic_ui/AssistantGenericUiModel.java

@@ -18,7 +18,7 @@ import org.chromium.ui.modelutil.PropertyModel;
 @JNINamespace("autofill_assistant")
 public class AssistantGenericUiModel extends PropertyModel {
     /** The view inflated by the generic UI framework. */
-    static final WritableObjectPropertyKey<View> VIEW = new WritableObjectPropertyKey<>();
+    public static final WritableObjectPropertyKey<View> VIEW = new WritableObjectPropertyKey<>();
 
     public AssistantGenericUiModel() {
         super(VIEW);