Support setting mouse cursor icon in Android N.

chrome/android/java/src/org/chromium/chrome/browser/tab/TabViewAndroidDelegate.java

 // Copyright 2017 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.
 
 package org.chromium.chrome.browser.tab;
 
+import android.os.Build;
+import android.view.PointerIcon;
 import android.view.ViewGroup;
 
 import org.chromium.ui.base.ViewAndroidDelegate;
 
 /**
  * Implementation of the abstract class {@link ViewAndroidDelegate} for Chrome.
  */
 class TabViewAndroidDelegate extends ViewAndroidDelegate {
     /** Used for logging. */
     private static final String TAG = "TabVAD";
@@ skipping 23 matching lines @@
 
     @Override
     public int getSystemWindowInsetBottom() {
         return mTab.getSystemWindowInsetBottom();
     }
 
     @Override
     public ViewGroup getContainerView() {
         return mContainerView;
     }
+
+    @Override
+    public void updatePointerIcon(PointerIcon icon) {
+        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.N) {
+            getContainerView().getRootView().setPointerIcon(icon);

[Ted C, 2017/06/07 19:27:18]

since this mutates the root view, what happens in cases where the tab crashes,
the tab is switched to another tab via a keyboard shortcut, the mouse is
disconnected, move focus outside of the view (i.e. it is full page textarea in
the web contents but you move to the omnibox, does it get reset)?

is this called often enough to reset to the initial value?  I just want to make
sure that we don't leave the cursor in a bad state ever.

[jaebaek, 2017/06/08 01:00:11]

It seems we cannot make the pointer icon visible by setting it in the container
view.
(as far as I tested, we must set it to parent of parent of container view)

When testing cases you mentioned:
tab crashes --> the pointer icon disappears.
(it becomes visible when I move it)
switch to another tab --> the same as tab crashes.
mouse disconnected --> the pointer icon remains around 10 seconds and
disappears.
move focus outside of the view --> it gets reset.

When observing its behavior:
move event --> it is updated quickly (almost realtime).
keyboard or touch event --> disappears after 1 second.
(during the short time until it disappears, it is updated if needed)
no event --> the pointer icon remains around 10 seconds and disappears.
(the same as mouse disconnected)

It looks fine, but I also dislike this hacky solution .. let me check why we
cannot change the pointer icon only by setting it to the container view.

+        }
+    }
 }