Extend the multidex logic to only kick in for the main browser application.

base/android/java/templates/ChromiumMultiDex.template

 // Copyright 2015 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.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;
 
 /**
  *  Performs multidex installation for non-isolated processes.
  */
 public class ChromiumMultiDex {
 
     private static final String TAG = "base_multidex";
 
+    private static final String IGNORE_MULTIDEX_KEY = ".ignore_multidex";

[nyquist, 2015/11/25 18:57:20]

Could you add a comment here referring to the value in the manifest?

[Ted C, 2015/11/25 19:14:11]

Done.

+
     /**
      *  Installs secondary dexes if possible/necessary.
      *
      *  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.
      */
     @VisibleForTesting
 #if defined(MULTIDEX_CONFIGURATION_Debug)
     public static void install(Context context) {
-        try {
-            // 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 && processIsIsolated()) {
-                Log.i(TAG, "Skipping multidex installation: inside isolated process.");
-            } else {
-                MultiDex.install(context);
-                Log.i(TAG, "Completed multidex installation.");
-            }
-        } catch (NoSuchMethodException e) {
-            Log.wtf(TAG, "Failed multidex installation", e);
-        } catch (IllegalAccessException e) {
-            Log.wtf(TAG, "Failed multidex installation", e);
-        } catch (InvocationTargetException e) {
-            Log.wtf(TAG, "Failed multidex installation", e);
+        // 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)) {

[jbudorick, 2015/11/25 18:13:35]

One other thing to consider: we could potentially only skip multidex extraction
rather than skipping installation entirely. This would involve reflecting into
the multidex support library, but it would let privileged processes use code
from secondary dexes without having to pay the extraction penalty every time.

[Ted C, 2015/11/25 18:17:15]

Maybe, but right now it doesn't seem we need anything from the secondary dexes,
so this seems like even more complication for stuff that is unneeded.

+            Log.i(TAG, "Skipping multidex installation: not needed for process.");
+        } else {
+            MultiDex.install(context);
+            Log.i(TAG, "Completed multidex installation.");
         }
     }
 
-    // Calls Process.isIsolated, a private Android API.
-    private static boolean processIsIsolated()
-            throws NoSuchMethodException, IllegalAccessException, InvocationTargetException {
-        return (boolean) Process.class.getMethod("isIsolated").invoke(null);
+    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);
+            return !appInfo.metaData.getBoolean(currentProcessName + IGNORE_MULTIDEX_KEY, false);
+        } catch (PackageManager.NameNotFoundException e) {
+            return true;
+        }
     }
 #else
     public static void install(Context context) {
     }
 #endif
 
 }