Revert "Change isBlock and isInline functions to check for isElementNode"

This reverts commit 6415003fe8070545c67d82f88c69512bd38b2f9f.
isElementNode() check added in isBlock() introduced a crash.
Hence reverting the same.

BUG=341783

Review URL: https://codereview.chromium.org/169403002

git-svn-id: svn://svn.chromium.org/blink/trunk@167362 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Improve key-related HTMLMediaElement exception messages.

BUG=270033

Review URL: https://codereview.chromium.org/166653004

git-svn-id: svn://svn.chromium.org/blink/trunk@167363 bbb929c8-8fbe-4397-9dbb-9b2b20218538