fragmentのタブのアイコン画像のサイズをカスタマイズする ref: http://qiita.com/matsuyoro/items/48399411cca6764e051b

design_fragment_icon_camera.xml

<ImageView xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    android:layout_width="48dp"
    android:layout_height="48dp"
    android:scaleType="centerInside"
    app:srcCompat="@drawable/ic_attachment_black_24dp"
    android:tint="@color/colorBlack"
    />

design_fragment_icon_line_weight.xml

<?xml version="1.0" encoding="utf-8"?>
<ImageView xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    android:layout_width="32dp"
    android:layout_height="32dp"
    android:scaleType="centerInside"
    android:src="@drawable/image_icon_line"
    />

FragmentActivity.java

TabLayout tabLayout = (TabLayout) findViewById(R.id.tabs);
tabLayout.setupWithViewPager(mViewPager);

tabLayout.getTabAt(0).setCustomView(R.layout.design_fragment_icon_camera);
tabLayout.getTabAt(1).setCustomView(R.layout.design_fragment_line_weight);