gin: Automatic conversion from JS number to intger

Now gin doesn't convert JavaScript double to an integer. This means that
gin::Arguments::GetNext() with a pointer of an integer fails when the
next arguments is double, and nothing is set to the vairable. IMO this
can cause bugs which are hard to understand. It is because on JavaScript
side we can't distinguish integer and double, and GetNext() with an
integer variable and JS number produces unstable results.

For example, In [1], EventSender's mouseMoveTo is called with arguments
which can be doubles, not integers, but EventSender::mouseToMove excepts
integers. Now EventSender is implemented by CppBoundClass and toInt32 is
used explicitly, but now EventSender is being moved to gin, and using
GetNext with integer vairables simply will fail.

[1] https://code.google.com/p/chromium/codesearch#chromium/src/third_party/WebKit/LayoutTests/fast/events/5056619.html&sq=package:chromium

BUG=331301
TEST=gin_unittests --gtest_filter=ConverterTest.Int32

Review URL: https://codereview.chromium.org/195893017

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@257105 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 257105
Mojo: Add a (failing) test for crbug.com/348644

(that data isn't changed underneath two-phase data pipe reads). And disable the
test, of course.

R=darin@chromium.org
BUG=348644

Review URL: https://codereview.chromium.org/196603017

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@257106 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 257106