Upstream: Extract "WebAPK service" implementation from Chrome APK

chrome/android/java/src/org/chromium/chrome/browser/webapps/WebApkVersionManager.java

+// Copyright 2016 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.webapps;
+
+import android.content.Context;
+import android.content.SharedPreferences;
+import android.preference.PreferenceManager;
+
+import org.chromium.base.FileUtils;
+import org.chromium.base.ThreadUtils;
+import org.chromium.webapk.lib.client.DexOptimizer;
+
+import java.io.File;
+
+/**
+ * Updates installed WebAPKs after a Chrome update.
+ */
+public class WebApkVersionManager {
+    /**
+     * Name of the shared preference to store whether an attempt to extract the WebAPK runtime
+     * library was made.
+     */
+    private static final String TRIED_EXTRACTING_DEX_PREF =
+            "web_apk_version_manager_tried_extracting_dex";
+
+    private static final String TAG = "WebApkVersionManager";
+
+    /**
+     * Tries to extract the WebAPK runtime dex from the Chrome APK if it has not tried already.
+     * Should not be called on UI thread.
+     * @param Context context
+     */
+    public static void updateWebApksIfNeeded(Context context) {
+        assert !ThreadUtils.runningOnUiThread();
+
+        // TODO(pkotwicz|hanxi): Detect whether the manifest of installed APKs needs to be updated.
+        // (crbug.com/604513)
+
+        SharedPreferences preferences =
+                PreferenceManager.getDefaultSharedPreferences(context.getApplicationContext());
+        if (preferences.getBoolean(TRIED_EXTRACTING_DEX_PREF, false)) {

[Xi Han, 2016/05/25 15:36:13]

Please move the comments in line 38 and 39 right above this "if" check. Or maybe
to have a function needToUpdate() and change the check from: 
if (preferences.getBoolean(TRIED_EXTRACTING_DEX_PREF, false)) to
if (!needToUpdate())
and move the comment to needToUpdate().

It is because that the above check always leads to an early exist, a little
confusing without a good explanation.

[pkotwicz, 2016/05/25 17:16:42]

I removed the comment entirely for now :)

+            return;
+        }
+
+        SharedPreferences.Editor editor = preferences.edit();
+        editor.putBoolean(TRIED_EXTRACTING_DEX_PREF, true);
+        editor.apply();
+
+        File dexDir = context.getDir("dex", Context.MODE_PRIVATE);
+        File dexFile = new File(dexDir, "web_apk.dex");
+        if (!FileUtils.extractAsset(context, "web_apk.dex", dexFile)
+                || !DexOptimizer.optimize(dexFile)) {
+            return;
+        }
+
+        // Make dex file world-readable so that WebAPK can use it.
+        dexFile.setReadable(true, false);
+    }
+}