android - How to change WebView text size

activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:id="@+id/rl"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:padding="10dp"
    tools:context=".MainActivity"
    android:background="#fcfdfb"
    >
    <SeekBar
        android:id="@+id/seek_bar"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:max="12"
        />
    <WebView
        android:id="@+id/web_view"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:layout_below="@id/seek_bar"
        />
</RelativeLayout>

MainActivity.java

package com.cfsuman.me.androidcodesnippets;

import android.app.Activity;
import android.content.Context;
import android.graphics.Bitmap;
import android.graphics.Color;
import android.graphics.drawable.ColorDrawable;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.Window;
import android.webkit.WebChromeClient;
import android.webkit.WebView;
import android.webkit.WebViewClient;
import android.widget.RelativeLayout;
import android.widget.SeekBar;


public class MainActivity extends AppCompatActivity {
    private Context mContext;
    private Activity mActivity;

    private RelativeLayout mRelativeLayout;
    private WebView mWebView;
    private SeekBar mSeekBar;

    private String mUrl="http://developer.android.com/guide/components/fundamentals.html";


    @Override
    protected void onCreate(Bundle savedInstanceState) {
        // Request window feature action bar
        requestWindowFeature(Window.FEATURE_ACTION_BAR);
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        // Get the application context
        mContext = getApplicationContext();
        // Get the activity
        mActivity = MainActivity.this;

        // Change the action bar color
        getSupportActionBar().setBackgroundDrawable(
                new ColorDrawable(Color.parseColor("#FF4E8C0F"))
        );

        // Get the widgets reference from XML layout
        mRelativeLayout = (RelativeLayout) findViewById(R.id.rl);
        mWebView = (WebView) findViewById(R.id.web_view);
        mSeekBar = (SeekBar) findViewById(R.id.seek_bar);

        // Request to render the web page
        renderWebPage(mUrl);

        // Set the initial progress of seek bar
        mSeekBar.setProgress(mWebView.getSettings().getTextZoom()/25);

        // Set a change listener for seek bar
        mSeekBar.setOnSeekBarChangeListener(new SeekBar.OnSeekBarChangeListener() {
            @Override
            public void onProgressChanged(SeekBar seekBar, int i, boolean b) {
                /*
                    public abstract void setTextZoom (int textZoom)
                        Sets the text zoom of the page in percent. The default is 100.

                    Parameters
                        textZoom : the text zoom in percent
                */

                // Zoom the web page text
                // We will allow text zooming 25% to 300%
                mWebView.getSettings().setTextZoom(i*25);
            }

            @Override
            public void onStartTrackingTouch(SeekBar seekBar) {

            }

            @Override
            public void onStopTrackingTouch(SeekBar seekBar) {

            }
        });

    }

    // Custom method to render a web page
    protected void renderWebPage(String urlToRender){
        mWebView.setWebViewClient(new WebViewClient() {
            @Override
            public void onPageStarted(WebView view, String url, Bitmap favicon) {
                // Do something on page loading started
                mUrl = url;
            }

            @Override
            public void onPageFinished(WebView view, String url) {
                // Do something when page loading finished
                mUrl = url;
            }
        });

        mWebView.setWebChromeClient(new WebChromeClient() {
            public void onProgressChanged(WebView view, int newProgress) {
            }
        });

        /*
            WebSettings
                Manages settings state for a WebView. When a WebView is first created, it obtains a
                set of default settings. These default settings will be returned from any getter
                call. A WebSettings object obtained from WebView.getSettings() is tied to the life
                of the WebView. If a WebView has been destroyed, any method call on WebSettings
                will throw an IllegalStateException.
        */
        // Enable the javascript
        mWebView.getSettings().setJavaScriptEnabled(true);

        // Render the web page
        mWebView.loadUrl(urlToRender);
    }
}