Steps to reproduce the problem:
1. Open the attached html files in Chrome for Android.

2. First example displays an input field aligned to the bottom of the page. If you tap it, onscreen keyboard will be displayed and the view will be resized so the input field will be shown above the onscreen keyboard. However, if you switch into fullscreen mode using the HTML5 fullscreen API and tap the input field, then it will be hidden behind the onscreen keyboard.

3. The second example displays many input fields. If you tap any of them near the bottom of the screen then it will be scrolled into view and shown above the onscreen keyboard. However, after switching into fullscreen mode when you tap the  input field it will be hidden behind the onscreen keyboard. Moreover, the view cannot be scrolled (dragged) to make the focused input field visible.

So there are two issues in fullscreen mode when onscreen keyboard is visible: the view's size is not updated and it cannot be scrolled.

What is the expected behavior?
Onscreen keyboard shouldn't hide the focused input field.

What went wrong?
Onscreen keyboard hides focused input field because the viewport's dimension is not updated AND it cannot be scrolled.

Did this work before? N/A 

Does this work in other browsers? N/A

Chrome version: 56.0.2924.87  Channel: stable
OS Version: 5.1.1
Flash Version: 

This issue is similar to  issue 453259 , but this is related to the Fullscreen API while  issue 453259  is related to webapps (standalone mode). That's why I was told to file this as a new issue.

Use cases:
HTML5 games use the fullscreen API to provide better user experiment. Fullscreen API is required even in webapps, because webapps currently start in standalone mode (status bar still visible).
HTML5 games might need text input for various reasons: user registration, character customization, in-game chat etc.
HTML5 game can be canvas based or built from regular HTML components (for instance a sports manager game does not need custom canvas GUI).

Workarounds:
Exit fullscreen mode if an input field receives focus / restore fullscreen mode if focus is lost (bad user experience).

Currently, there is no way client-code javascript can determine if onscreen keyboard is displayed in fullscren or not because viewport dimensions are not updated.
In comparison, Firefox for Android updates viewport dimensions so the first example is working. Scrolling is broken in Firefox too (second example).
 

Deleted: crosk.html 1.0 KB

crosk.html 1.0 KB View Download

Deleted: crosk2.html 1.5 KB

crosk2.html 1.5 KB View Download