[Autofill Assistant] Allow user to swipe down the assistant UI.

Avoid blocking important part of the underlying page.

Screenshots:
https://drive.google.com/file/d/1QHMmX0s2uIE1v82TNmj7KwR-3PJIipGO/view?usp=sharing
https://drive.google.com/file/d/13EipCdWx5sJDn8-BTeS9f3vb_v5poJQA/view?usp=sharing

Bug: 119282188
Change-Id: I4a5c5144f0dd4ef6803c270129d18cb716438a17
Reviewed-on: https://chromium-review.googlesource.com/c/1340940Reviewed-by: Ted Choc <tedchoc@chromium.org>
Reviewed-by: Ganggui Tang <gogerald@chromium.org>
Commit-Queue: Hui Wu <wuandy@chromium.org>
Cr-Commit-Position: refs/heads/master@{#612344}

chrome/android/java/res_autofill_assistant/drawable/autofill_assistant_swipe_indicator.xml

+<?xml version="1.0" encoding="utf-8"?>
+<!-- Copyright 2018 The Chromium Authors. All rights reserved.
+     Use of this source code is governed by a BSD-style license that can be
+     found in the LICENSE file. -->
+<shape
+    xmlns:android="http://schemas.android.com/apk/res/android"
+    android:shape="rectangle">
+  <solid android:color="@color/autofill_assistant_light_grey"/>
+  <corners android:radius="2dp"/>
+  <size android:height="4dp" android:width="36dp"/>
+</shape>

chrome/android/java/res_autofill_assistant/values-v17/colors.xml

@@ -10,4 +10,5 @@
     Please see src/ui/android/java/res/values/colors.xml for the shared common colors.
     -->
     <color name="autofill_assistant_light_blue">#e9f0fd</color>
+    <color name="autofill_assistant_light_grey">@color/modern_grey_300</color>
 </resources>

chrome/android/java/src/org/chromium/chrome/browser/autofill_assistant/AutofillAssistantUiDelegate.java

@@ -19,6 +19,7 @@ import android.media.ThumbnailUtils;
 import android.support.annotation.ColorInt;
 import android.support.annotation.IntDef;
 import android.support.annotation.Nullable;
+import android.support.design.widget.BottomSheetBehavior;
 import android.support.v4.graphics.drawable.RoundedBitmapDrawable;
 import android.support.v4.graphics.drawable.RoundedBitmapDrawableFactory;
 import android.support.v4.text.TextUtilsCompat;
@@ -92,6 +93,7 @@ class AutofillAssistantUiDelegate {
     private final View mFullContainer;
     private final TouchEventFilter mTouchEventFilter;
     private final LinearLayout mBottomBar;
+    private final BottomSheetBehavior mBottomBarBehavior;
     private final HorizontalScrollView mCarouselScroll;
     private final ViewGroup mChipsViewContainer;
     private final TextView mStatusMessageView;
@@ -255,6 +257,7 @@ class AutofillAssistantUiDelegate {
         // TODO(crbug.com/806868): Set hint text on overlay.
         mTouchEventFilter = (TouchEventFilter) mFullContainer.findViewById(R.id.touch_event_filter);
         mBottomBar = mFullContainer.findViewById(R.id.bottombar);
+        mBottomBarBehavior = BottomSheetBehavior.from(mBottomBar);
         mBottomBar.findViewById(R.id.close_button)
                 .setOnClickListener(unusedView -> mClient.onDismiss());
         mBottomBar.findViewById(R.id.feedback_button)
@@ -423,6 +426,7 @@ class AutofillAssistantUiDelegate {
             mTouchEventFilter.init(mClient, mActivity.getFullscreenManager(),
                     mActivity.getActivityTab().getWebContents());
             mFullContainer.setVisibility(View.VISIBLE);
+            mBottomBarBehavior.setState(BottomSheetBehavior.STATE_EXPANDED);
 
             // Announce Autofill Assistant is available for accessibility.
             mBottomBar.announceForAccessibility(