Use drawBidiText for RenderImage Alt Text

Change RenderImage::paintReplaced to use context::drawBidiText instead
of context::drawText. This negates the need for the changes in r163930
to RenderBlockFlow::constructTextRunInternal and thus reverts that
change. Calling drawBidiText instead ensures that the directionality is
respected through the string.

BUG=326921
TEST=fast/text/bidi-img-alt-text.html
R=eseidel@chromium.org

Review URL: https://codereview.chromium.org/93713003

git-svn-id: svn://svn.chromium.org/blink/trunk@164388 bbb929c8-8fbe-4397-9dbb-9b2b20218538