Probably the same root cause as  issue 776655 

Confirmed, it's the same thing as  issue 776655 . After crrev.com/c/700443, the embeddedSearch APIs can still be called directly, like
window.chrome.embeddedSearch.searchBox.startCapturingKeyStrokes();
but the following does not work (it did work before):
var f = window.chrome.embeddedSearch.searchBox.startCapturingKeyStrokes;
f();

Calling f fails with the following error:
Uncaught TypeError: Error processing argument at index -1, conversion failure from undefined

Jochen, any idea what's up with that?

hum, what's f() supposed to do? When I look at the implementation of startCapturingKeyStrokes() it accesses "this" to get the render frame. invoking f() is basically invoking the method without the "this" project, and gin protects against that.

f() should call the native SearchBoxBindings::StartCapturingKeyStrokes method (which does use "this", the C++ one). I guess by first assigning to a JS var, the JS "this" gets lost. The following does work:
var f2 = window.chrome.embeddedSearch.searchBox.startCapturingKeyStrokes.bind(window.chrome.embeddedSearch.searchBox);
f2();

This kinda makes sense, but the problem is that the previous (v8::Extension) implementation did not require the bind(), and it's used in that way. Is there any way to make the gin implementation behave the same way?

if you want to be able to invoke the function without binding it to the object, the C++ function needs to be static. You probably then have to use blink::WebLocalFrame::FrameForCurrentContex() to get the frame and go from there.

Alright, thanks! I'll get on that and hopefully send you a CL soon.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/453cdca9a87018ae26b911899beb6394eaa17ecd

commit 453cdca9a87018ae26b911899beb6394eaa17ecd
Author: Marc Treib <treib@chromium.org>
Date: Fri Oct 20 11:29:19 2017

embeddedSearch API: Expose static functions

This makes sure they can be called after being assigned to a var, like
var f = chrome.embeddedSearch.searchBox.startCapturingKeyStrokes;
f();

This was the case when the API was implemented as a v8::Extension, but
got broken when it was converted to Gin in crrev.com/c/700443.

Bug:  776660 ,  776655 
Change-Id: Idab6a6e960ff614c80f74b3acdadede7bf9af9d0
Reviewed-on: https://chromium-review.googlesource.com/730186
Reviewed-by: Jochen Eisinger <jochen@chromium.org>
Commit-Queue: Marc Treib <treib@chromium.org>
Cr-Commit-Position: refs/heads/master@{#510401}
[modify] https://crrev.com/453cdca9a87018ae26b911899beb6394eaa17ecd/chrome/browser/ui/search/local_ntp_browsertest.cc
[modify] https://crrev.com/453cdca9a87018ae26b911899beb6394eaa17ecd/chrome/renderer/chrome_render_frame_observer.cc
[modify] https://crrev.com/453cdca9a87018ae26b911899beb6394eaa17ecd/chrome/renderer/searchbox/searchbox_extension.cc
[modify] https://crrev.com/453cdca9a87018ae26b911899beb6394eaa17ecd/chrome/renderer/searchbox/searchbox_extension.h