Context menu key should set event target to the focused element.

This patch adds a regression test for behavior that was fixed in Chrome between
version 35 and 37. Steps to reproduce:

1) Set an event handler for context menu on the document:

  document.addEventListener('contextmenu', function(e) {
    console.log(e.target.id);
    e.preventDefault();
  }, true);

2) Focus a div in the document:

  <div id="anchor" tabindex="0">Target</div>

3) Press the context menu key.

Expected: The console should print 'anchor', because the event target is the
div, not the document.

Observed (in version 35): The console prints '', because the event target was
the document.

BUG=381996
TEST=LayoutTests/fast/events/menu-key-context-menu-document.html

Review URL: https://codereview.chromium.org/329493002

git-svn-id: svn://svn.chromium.org/blink/trunk@177769 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Expose isEmailField() for input element

Motivation is to replace instances of "element.formControlType() == WebString::fromUTF8("email")" with isEmailField().

BUG=None

Review URL: https://codereview.chromium.org/375313002

git-svn-id: svn://svn.chromium.org/blink/trunk@177770 bbb929c8-8fbe-4397-9dbb-9b2b20218538