[StartSurface] Return to last active pane

Bug: 982018

Change-Id: I28705cff7085007ece4a802e03409f95996c3103
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1745572
Commit-Queue: Mia Glaese <glamia@chromium.org>
Reviewed-by: Wei-Yin Chen (陳威尹) <wychen@chromium.org>
Reviewed-by: Ganggui Tang <gogerald@chromium.org>
Cr-Commit-Position: refs/heads/master@{#689943}

chrome/android/features/start_surface/internal/BUILD.gn

@@ -80,6 +80,7 @@ android_library("java") {
     "java/src/org/chromium/chrome/features/start_surface/BottomBarCoordinator.java",
     "java/src/org/chromium/chrome/features/start_surface/BottomBarView.java",
     "java/src/org/chromium/chrome/features/start_surface/BottomBarViewBinder.java",
+    "java/src/org/chromium/chrome/features/start_surface/ReturnToStartSurfaceUtil.java",
     "java/src/org/chromium/chrome/features/start_surface/StartSurfaceCoordinator.java",
     "java/src/org/chromium/chrome/features/start_surface/StartSurfaceDelegate.java",
     "java/src/org/chromium/chrome/features/start_surface/StartSurfaceLayout.java",

chrome/android/features/start_surface/internal/java/src/org/chromium/chrome/features/start_surface/ReturnToStartSurfaceUtil.java

+// Copyright 2019 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.features.start_surface;
+
+import android.content.Context;
+import android.content.SharedPreferences;
+
+import org.chromium.base.ContextUtils;
+
+/**
+ * This is a utility class for managing the start surface when returning to Chrome.
+ */
+public final class ReturnToStartSurfaceUtil {
+    /** Preference to indicate whether explore pane was visible last in the start surface.*/
+    private static final String START_SURFACE_PREF_FILE_NAME = "start_surface";
+    private static final String EXPLORE_SURFACE_VISIBLE_LAST = "explore_surface_visible_last";
+
+    private ReturnToStartSurfaceUtil() {}
+
+    /**
+     * Determine if we should show the explore surface on returning to Chrome.
+     * @return whether the last pane shown in StartSurface was explore
+     */
+    public static boolean shouldShowExploreSurface() {
+        return getSharedPreferences().getBoolean(EXPLORE_SURFACE_VISIBLE_LAST, false);
+    }
+
+    /**
+     * Preserve whether last active pane in the start surface was the explore surface.
+     * @param isVisible whether the explore surface is visible
+     */
+    public static void setExploreSurfaceVisibleLast(boolean isVisible) {
+        getSharedPreferences().edit().putBoolean(EXPLORE_SURFACE_VISIBLE_LAST, isVisible).apply();
+    }
+
+    private static SharedPreferences getSharedPreferences() {
+        return ContextUtils.getApplicationContext().getSharedPreferences(
+                START_SURFACE_PREF_FILE_NAME, Context.MODE_PRIVATE);
+    }
+}

chrome/android/features/start_surface/internal/java/src/org/chromium/chrome/features/start_surface/StartSurfaceMediator.java

@@ -101,6 +101,15 @@ class StartSurfaceMediator
 
             // Set the initial state.
             updateIncognitoMode(tabModelSelector.isIncognitoSelected());
+
+            // Show explore surface if in TWO PANES mode and last visible pane was explore.
+            if (!onlyShowExploreSurface) {
+                boolean shouldShowExploreSurface =
+                        ReturnToStartSurfaceUtil.shouldShowExploreSurface();
+                mPropertyModel.set(IS_EXPLORE_SURFACE_VISIBLE, shouldShowExploreSurface);
+                mPropertyModel.set(
+                        BOTTOM_BAR_SELECTED_TAB_POSITION, (shouldShowExploreSurface ? 1 : 0));
+            }
         }
 
         mController.addOverviewModeObserver(this);
@@ -249,6 +258,7 @@ class StartSurfaceMediator
         // Update the 'BOTTOM_BAR_SELECTED_TAB_POSITION' property to reflect the change. This is
         // needed when clicking back button on the explore surface.
         mPropertyModel.set(BOTTOM_BAR_SELECTED_TAB_POSITION, isVisible ? 1 : 0);
+        ReturnToStartSurfaceUtil.setExploreSurfaceVisibleLast(isVisible);
     }
 
     private void updateIncognitoMode(boolean isIncognito) {
@@ -274,4 +284,4 @@ class StartSurfaceMediator
         if (feedSurfaceCoordinator != null) feedSurfaceCoordinator.destroy();
         mPropertyModel.set(FEED_SURFACE_COORDINATOR, null);
     }
-}
\ No newline at end of file
+}