Crash fix: RenderWidgetHostViewMac::SetBounds() can handle views removed from view hierarchy.

BUG=345970
TEST=Repro steps no longer cause crash, and expected behavior is correct.
R=ccameron@chromium.org

Review URL: https://codereview.chromium.org/175513007

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@253059 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 253059