Fixing crash when drawing accessibility focus indicator.

1. Added a lacking null check for the accessibility node
   info returned by an accessibility node provider. If
   the provider implementation is not correct this may
   happen.

2. Added clearing of the current accessibility focused
   node when the window focus changes. Now it is cleared
   in every case and if it happens that accessibility is
   enabled when the window gets focus, the accessibility
   focus will be properly set.

bug:6381296

Change-Id: Ieea1b07762745e6d932fc4ed4febfe77760b25b7

Author: sganov

core/java/android/view/ViewRootImpl.java

@@ -634,6 +634,8 @@ public void setView(View view, WindowManager.LayoutParams attrs, View panelParen
                 if (view.getImportantForAccessibility() == View.IMPORTANT_FOR_ACCESSIBILITY_AUTO) {
                     view.setImportantForAccessibility(View.IMPORTANT_FOR_ACCESSIBILITY_YES);
                 }
+
+                setAccessibilityFocusedHost(null);
             }
         }
     }
@@ -2326,6 +2328,9 @@ private void drawAccessibilityFocusedDrawableIfNeeded(Canvas canvas) {
             if (mAccessibilityFocusedVirtualView == null) {
                 mAccessibilityFocusedVirtualView = provider.findAccessibilitiyFocus(View.NO_ID);
             }
+            if (mAccessibilityFocusedVirtualView == null) {
+                return;
+            }
             mAccessibilityFocusedVirtualView.getBoundsInScreen(bounds);
             bounds.offset(-mAttachInfo.mWindowLeft, -mAttachInfo.mWindowTop);
         }
@@ -2849,6 +2854,8 @@ public void handleMessage(Message msg) {
                         mHasHadWindowFocus = true;
                     }
 
+                    setAccessibilityFocusedHost(null);
+
                     if (mView != null && mAccessibilityManager.isEnabled()) {
                         if (hasWindowFocus) {
                             mView.sendAccessibilityEvent(
@@ -2867,9 +2874,6 @@ public void handleMessage(Message msg) {
                             if (mAccessibilityFocusedHost == null) {
                                 mView.requestAccessibilityFocus();
                             }
-                        } else {
-                            // Clear accessibility focus when the window loses input focus.
-                            setAccessibilityFocusedHost(null);
                         }
                     }
                 }