[Chrome Home] Mute background views for accessibility tab switcher

The changes make CompositorViewHolder not focusable and
OverviewListLayout not important when there is some view obscuring tabs.

Bug: 739382
Change-Id: I7739e25c31a659aae435c4e16313378caf7c4529
Reviewed-on: https://chromium-review.googlesource.com/679620Reviewed-by: Theresa <twellington@chromium.org>
Reviewed-by: Ted Choc <tedchoc@chromium.org>
Commit-Queue: Becky Zhou <huayinz@chromium.org>
Cr-Commit-Position: refs/heads/master@{#504182}

chrome/android/java/src/org/chromium/chrome/browser/ChromeTabbedActivity.java

@@ -117,6 +117,7 @@ import org.chromium.chrome.browser.toolbar.ToolbarControlContainer;
 import org.chromium.chrome.browser.util.FeatureUtilities;
 import org.chromium.chrome.browser.util.IntentUtils;
 import org.chromium.chrome.browser.vr_shell.VrShellDelegate;
+import org.chromium.chrome.browser.widget.OverviewListLayout;
 import org.chromium.chrome.browser.widget.ViewHighlighter;
 import org.chromium.chrome.browser.widget.bottomsheet.BottomSheet;
 import org.chromium.chrome.browser.widget.bottomsheet.BottomSheet.StateChangeReason;
@@ -2023,6 +2024,37 @@ public class ChromeTabbedActivity
         return mLayoutManager != null && mLayoutManager.overviewVisible();
     }
 
+    /**
+     * Update focus and accessibility importance for background view when accessibility tab switcher
+     * is used in Chrome Home.
+     */
+    private void updateAccessibilityVisibility() {
+        if (getBottomSheet() == null || mLayoutManager == null) return;
+
+        CompositorViewHolder compositorViewHolder = getCompositorViewHolder();
+        if (compositorViewHolder != null) {
+            compositorViewHolder.setFocusable(!isViewObscuringAllTabs());
+        }
+
+        OverviewListLayout overviewListLayout =
+                (OverviewListLayout) mLayoutManager.getOverviewListLayout();
+        if (overviewListLayout != null) {
+            overviewListLayout.updateAccessibilityVisibility(!isViewObscuringAllTabs());
+        }
+    }
+
+    @Override
+    public void addViewObscuringAllTabs(View view) {
+        super.addViewObscuringAllTabs(view);
+        updateAccessibilityVisibility();
+    }
+
+    @Override
+    public void removeViewObscuringAllTabs(View view) {
+        super.removeViewObscuringAllTabs(view);
+        updateAccessibilityVisibility();
+    }
+
     @Override
     protected IntentHandlerDelegate createIntentHandlerDelegate() {
         return new InternalIntentDelegate();

chrome/android/java/src/org/chromium/chrome/browser/widget/OverviewListLayout.java

@@ -8,6 +8,7 @@ import android.content.Context;
 import android.view.LayoutInflater;
 import android.view.View;
 import android.view.ViewGroup;
+import android.view.accessibility.AccessibilityEvent;
 import android.widget.FrameLayout;
 import android.widget.ListView;
 
@@ -209,4 +210,21 @@ public class OverviewListLayout extends Layout implements AccessibilityTabModelA
     protected SceneLayer getSceneLayer() {
         return mSceneLayer;
     }
+
+    /**
+     * Set whether or not the accessibility tab switcher is visible (from an accessibility
+     * perspective), or whether it is obscured by another view.
+     * @param isVisible Whether or not accessibility tab switcher is visible.
+     */
+    public void updateAccessibilityVisibility(boolean isVisible) {
+        if (mTabModelWrapper == null) return;
+
+        int importantForAccessibility = isVisible
+                ? View.IMPORTANT_FOR_ACCESSIBILITY_AUTO
+                : View.IMPORTANT_FOR_ACCESSIBILITY_NO_HIDE_DESCENDANTS;
+        if (mTabModelWrapper.getImportantForAccessibility() != importantForAccessibility) {
+            mTabModelWrapper.setImportantForAccessibility(importantForAccessibility);
+            mTabModelWrapper.sendAccessibilityEvent(AccessibilityEvent.TYPE_WINDOW_CONTENT_CHANGED);
+        }
+    }
 }