boot setup default Launcher

1.add intent category in app mainfest

<intent-filter>
    <action android:name="android.intent.action.MAIN" />
    <category android:name="android.intent.category.HOME" />
    <category android:name="android.intent.category.DEFAULT" />
    <category android:name="android.intent.category.maozen.home" />
    <!-- "android.intent.category.maozen.home" this is the sample category，
    use it diffrent to others Launcher -->
</intent-filter>

2. modify frameworks/base/services/core/java/com/android/server/am/ActivityManagerService.java

    Intent getHomeIntent() {
        Intent intent = new Intent(mTopAction, mTopData != null ? Uri.parse(mTopData) : null);
        intent.setComponent(mTopComponent);
        intent.addFlags(Intent.FLAG_DEBUG_TRIAGED_MISSING);
        if (mFactoryTest != FactoryTest.FACTORY_TEST_LOW_LEVEL) {
            intent.addCategory(Intent.CATEGORY_HOME);
        }
        return intent;
    }
    /*
    * our Intent addCategory
    */
    Intent getMaozenHomeIntent() {
        Intent intent = new Intent(mTopAction, mTopData != null ? Uri.parse(mTopData) : null);
        intent.setComponent(mTopComponent);
        intent.addFlags(Intent.FLAG_DEBUG_TRIAGED_MISSING);
        if (mFactoryTest != FactoryTest.FACTORY_TEST_LOW_LEVEL) {
        intent.addCategory("android.intent.category.maozen.home");
            intent.addCategory(Intent.CATEGORY_HOME);
        }
        return intent;
    }

    boolean startHomeActivityLocked(int userId, String reason) {
        if (mFactoryTest == FactoryTest.FACTORY_TEST_LOW_LEVEL
                && mTopAction == null) {
            // We are running in factory test mode, but unable to find
            // the factory test app, so just sit around displaying the
            // error message and don't try to start anything.
            return false;
        }
            //filter ouer Launcher first
        Intent intent = getMaozenHomeIntent();
        ActivityInfo aInfo = resolveActivityInfo(intent, STOCK_PM_FLAGS, userId);
        //then if null，filter system default Launcher 
        if(aInfo==null){
        intent = getHomeIntent();
            aInfo = resolveActivityInfo(intent, STOCK_PM_FLAGS, userId);
        }
        if (aInfo != null) {
            intent.setComponent(new ComponentName(aInfo.applicationInfo.packageName, aInfo.name));
            // Don't do this if the home app is currently being
            // instrumented.
            aInfo = new ActivityInfo(aInfo);
            aInfo.applicationInfo = getAppInfoForUser(aInfo.applicationInfo, userId);
            ProcessRecord app = getProcessRecordLocked(aInfo.processName,
                    aInfo.applicationInfo.uid, true);
            if (app == null || app.instrumentationClass == null) {
                intent.setFlags(intent.getFlags() | Intent.FLAG_ACTIVITY_NEW_TASK);
                mActivityStarter.startHomeActivityLocked(intent, aInfo, reason);
            }
        } else {
            Slog.wtf(TAG, "No home screen found for " + intent, new Throwable());
        }

        return true;
    }