First set of changes to remove ENABLE_TOUCH_ICON_LOADING compile time flag.
Add TouchIconLoading runtime and the equivalent WebRuntimeFeature API.

BUG=332863

Review URL: https://codereview.chromium.org/132163002

git-svn-id: svn://svn.chromium.org/blink/trunk@164808 bbb929c8-8fbe-4397-9dbb-9b2b20218538