[Chromium] Implement a Layout Test for editing/SurroundingText

[Chromium] Implement a Layout Test for editing/SurroundingText
https://bugs.webkit.org/show_bug.cgi?id=82461

Reviewed by Ryosuke Niwa.

Source/WebKit/chromium:

Allow passing nodes as arguments for layout test methods.

* public/WebBindings.h:
(WebBindings):
* src/WebBindings.cpp:
(WebKit::getNodeImpl):
(WebKit):
(WebKit::WebBindings::getNode):

Tools:

Add a new method to the layout test controller in order to retrieve the
text surrounding a provided element.

* DumpRenderTree/chromium/LayoutTestController.cpp:
(LayoutTestController::LayoutTestController):
(LayoutTestController::textSurroundingElement):
* DumpRenderTree/chromium/LayoutTestController.h:
(LayoutTestController):

LayoutTests:

Add a new layout test for the surrounding text feature.

* platform/chromium/editing/surrounding-text/surrounding-text-expected.txt: Added.
* platform/chromium/editing/surrounding-text/surrounding-text.html: Added.

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@121713 268f45cc-cd09-0410-ab3c-d52691b4dbfc