Revert of [Android] Rework multidex and enable multidex for unit_tests_apk.

base/android/java/templates/ChromiumMultiDex.template

Index: base/android/java/templates/ChromiumMultiDex.template
diff --git a/base/android/java/templates/ChromiumMultiDex.template b/base/android/java/templates/ChromiumMultiDex.template
index 7e70701c76a944e37d742b16b8cd002adac18366..5580489cd53980d322d294713f10dcbdc7143f65 100644
--- a/base/android/java/templates/ChromiumMultiDex.template
+++ b/base/android/java/templates/ChromiumMultiDex.template
@@ -4,22 +4,115 @@
 
 package org.chromium.base.multidex;
 
+import android.app.ActivityManager;
+import android.app.ActivityManager.RunningAppProcessInfo;
+import android.content.Context;
+import android.content.pm.ApplicationInfo;
+import android.content.pm.PackageManager;
+import android.os.Build;
+import android.os.Process;
+import android.support.multidex.MultiDex;
+
+import org.chromium.base.Log;
+import org.chromium.base.VisibleForTesting;
+
+import java.lang.reflect.InvocationTargetException;
+import java.lang.reflect.Method;
+
 /**
- *  Multidex configuration. Generated on a per-target basis.
+ *  Performs multidex installation for non-isolated processes.
  */
-class ChromiumMultiDex {
+public class ChromiumMultiDex {
 
-    /** Whether multidex is enabled for this target.
+    private static final String TAG = "base_multidex";
+
+    /**
+     * Suffix for the meta-data tag in the AndroidManifext.xml that determines whether loading
+     * secondary dexes should be skipped for a given process name.
+     */
+    private static final String IGNORE_MULTIDEX_KEY = ".ignore_multidex";
+
+    /**
+     *  Installs secondary dexes if possible/necessary.
      *
-     *  This has to be a function instead of a static final boolean s.t. the initial false value
-     *  doesn't get optimized into {@link ChromiumMultiDexInstaller} at base_java compile time.
+     *  Isolated processes (e.g. renderer processes) can't load secondary dex files on
+     *  K and below, so we don't even try in that case.
+     *
+     *  In release builds, this is a no-op because:
+     *    - multidex isn't necessary in release builds because we run proguard there and
+     *      thus aren't threatening to hit the dex limit; and
+     *    - calling MultiDex.install, even in the absence of secondary dexes, causes a
+     *      significant regression in start-up time (crbug.com/525695).
+     *
+     *  @param context The application context.
      */
-    static boolean isMultidexEnabled() {
-#if defined(ENABLE_MULTIDEX)
-        return true;
-#else
-        return false;
-#endif
+    @VisibleForTesting
+#if defined(MULTIDEX_CONFIGURATION_Debug)
+    public static void install(Context context) {
+        // TODO(jbudorick): Back out this version check once support for K & below works.
+        // http://crbug.com/512357
+        if (Build.VERSION.SDK_INT < Build.VERSION_CODES.LOLLIPOP
+                && !shouldInstallMultiDex(context)) {
+            Log.i(TAG, "Skipping multidex installation: not needed for process.");
+        } else {
+            MultiDex.install(context);
+            Log.i(TAG, "Completed multidex installation.");
+        }
     }
 
+    private static String getProcessName(Context context) {
+        try {
+            String currentProcessName = null;
+            int pid = android.os.Process.myPid();
+
+            ActivityManager manager =
+                    (ActivityManager) context.getSystemService(Context.ACTIVITY_SERVICE);
+            for (RunningAppProcessInfo processInfo : manager.getRunningAppProcesses()) {
+                if (processInfo.pid == pid) {
+                    currentProcessName = processInfo.processName;
+                    break;
+                }
+            }
+
+            return currentProcessName;
+        } catch (SecurityException ex) {
+            return null;
+        }
+    }
+
+    // Determines whether MultiDex should be installed for the current process.  Isolated
+    // Processes should skip MultiDex as they can not actually access the files on disk.
+    // Privileged processes need ot have all of their dependencies in the MainDex for
+    // performance reasons. 
+    private static boolean shouldInstallMultiDex(Context context) {
+        try {
+            Method isIsolatedMethod =
+                    android.os.Process.class.getMethod("isIsolated");
+            Object retVal = isIsolatedMethod.invoke(null);
+            if (retVal != null && retVal instanceof Boolean && ((Boolean) retVal)) {
+                return false;
+            }
+        } catch (IllegalAccessException | IllegalArgumentException
+                | InvocationTargetException | NoSuchMethodException e) {
+            // Ignore and fall back to checking the app processes.
+        }
+
+        String currentProcessName = getProcessName(context);
+        if (currentProcessName == null) return true;
+        
+        PackageManager packageManager = context.getPackageManager();
+        try {
+            ApplicationInfo appInfo = packageManager.getApplicationInfo(context.getPackageName(),
+                    PackageManager.GET_META_DATA);
+            if (appInfo == null || appInfo.metaData == null) return true;
+            return !appInfo.metaData.getBoolean(currentProcessName + IGNORE_MULTIDEX_KEY, false);
+        } catch (PackageManager.NameNotFoundException e) {
+            return true;
+        }
+    }
+#else
+    public static void install(Context context) {
+    }
+#endif
+
 }