[Spellcheck] Fix for bug when marker disappears from misspelled word causing it not to be replaced with selected word.

After context clicking a word misspelled based context, the marker would disappear from it. This is because upon clicking, a new spellcheck call would invoke and result in a grammar check on that single word without context, causing the spelling service to reply that it wasn't misspelled (since it couldn't identify it as misspelled without context). The fix is to force it to ignore grammar checking on single words and assume that the previous context-based spellcheck was correct.

Also adding LayoutTest to detect when a misspelled word is not replaced. LayoutTest passes with fix, but does not without it. In order to make the LayoutTest work, we needed more control over the timing and therefore moved the finishJSTest() method out of the initSpellTest and now call it at the end of each test.

BUG=303807

Review URL: https://codereview.chromium.org/89773003

git-svn-id: svn://svn.chromium.org/blink/trunk@163891 bbb929c8-8fbe-4397-9dbb-9b2b20218538