Gmail interface is really cool and mostly visited by so many users across the world, I have seen people browsing web and one page which keep opened all the time in one of the browser tab is gmail. Almost 99 people out 100 use google for search in the region of the world I live in, so when asked many users would love to search on google from inside gmail interface if it is possible, that would prevent opening a new tab for it.
Follow the procedure to enable google search inside gmail interface
1. Go to gmail.com and login to your account and go to gmail settings by clicking the link on the top right corner of the page.
2. Under settings, click the labs link to explore the labs features, scroll down and locate Google Search and Enable by checking the option to enable it as shown in the image below.
3. Once you select the enable option, scroll down to locate the button Save Changes and click it.
Once you have enabled this option, you will see small google search box on the left sidebar in gmail, from where you can search on google inside gmail interface as shown in the image below.
When you search, there will be a small pop kind of window, showing up the google search results in the gmail interface only on the same page as shown in the image below.
This is how you can search google inside gmail webmail interface, to open any search result in a new tab just click it.