Google Nexus 7 supports dictation and users can use this feature by tapping the microphone option on the Keyboard. Listed below are the steps to get back the microphone icon if it is missing from the device keyboard.
Step 1: Tap the Settings icon on the device.
Step 2: In the Settings screen, Tap the Language & input option available under Personal section.
Step 3: In the Language & input screen, navigate to Keyboard & Input methods and mark the checkbox with caption as Google voice typing
Now the Google Nexus 7 device must have the mic symbol as shown below.