Image decoding: Remove deprecated code path

Code that uses discardable memory on Android is now deprecated. Image
cache is moved to Skia and we can remove the deprecated code safely.

Deleted about 500 lines of code.

Review URL: https://codereview.chromium.org/489323002

git-svn-id: svn://svn.chromium.org/blink/trunk@180744 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Fix touch scrolling of main frame scrollbars

Touch adjustment isn't aware of scrollbars, so we bail out of touch
adjustment for gesture events that occur directly on top of a scrollbar
in bestClickableNodeForHitTestResult.  In r177164 I broke this for the
main frame scrollbar case by moving the main-frame scrollbar check
from before touch adjustment to after it.

This fixes the issue by moving the check back to just after the hit
test.

BUG=403744

Review URL: https://codereview.chromium.org/492933002

git-svn-id: svn://svn.chromium.org/blink/trunk@180745 bbb929c8-8fbe-4397-9dbb-9b2b20218538