Move global function intersectsNode() to local function in FrameSelection.cpp

Move global function intersectsNode() to local function in FrameSelection.cpp

This patch moves global function |intersectsNode()| in
"VisibleSelection.{cpp,h}" to local function in "FrameSelection.cpp" to
narrow visibility for improving code health and ease of implement composed tree
version.

This patch is a preparation of making selection to handle granularity for web
component, http://crrev.com/1277863002

BUG=513568
TEST=n/a; No behavior changes

Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=201362

[yosin_UTC9, 2015-08-28 01:52:16]

yosin@chromium.org changed reviewers:
+ hajimehoshi@chromium.org, yoichio@chromium.org

[yosin_UTC9, 2015-08-28 01:53:03]

PTAL

[yoichio, 2015-08-28 01:56:26]

lgtm

[yosin_UTC9, 2015-08-28 02:11:42]

The CQ bit was checked by yosin@chromium.org

[commit-bot: I haz the power, 2015-08-28 02:11:46]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1318183002/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1318183002/1

[commit-bot: I haz the power, 2015-08-28 03:15:46]

Committed patchset #1 (id:1) as
https://src.chromium.org/viewvc/blink?view=rev&revision=201362