inconsistent zooming in browser - keyboard vs gesture

[doniks]

I can zoom in a browser window with pinch gesture and I can zoom with Ctrl+/Ctrl- but this seem to be /separate zooming modes/, which is very confusing.

Reproduction:
- Nexus 7
- attach usb keyboard and mouse
- make a pinch gesture on a website, e.g. bugs.launchpad.net
=> website zooms in and out : OK

- press Ctrl- (control key and minus key)
=> website zooms out : OK

- zoom in with a pinch gesture to /undo/ the Ctrl- zoom
=> you can tell that there is a different /kind/ of zooming going on, the layout of the website becomes distorted : NOT OK

- try to zoom in with the keyboard, on "English (US)" keyboard layout, you must press the shift key to produce a plus sign, press Ctrl/Shift/=
=> nothing happens: NOT OK, I expect to zoom in

- switch the external keyboard layout to "German". here a plus can be typed without shift key, press Ctrl+
=> zooms in : OK

- hold Ctrl key down and use the scroll wheel
=> nothing happens : NOT OK, I expect to zoom in and out this way

(I'm happy to make separate bugs wrt mouse wheel and keyboard layout if requested.)