mac: History swiping shouldn't trust NSEvents to be sane.

Sometimes, even while a user is still in the middle of a gesture,
Cocoa starts sending momentum scroll wheel events instead of
gesture scroll events.

Add further safety checks to make sure that the events are coming from a
gesture.

BUG=138175
Test=None

Review URL: https://codereview.chromium.org/113993005

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@241776 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 241776
Remove |view_size_| from JniFrameConsumer

It isn't needed, since it always matches the size of the allocated Java
bitmap.

Review URL: https://codereview.chromium.org/93873016

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@241777 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 241777