Fix for Selection and showing context menu in the IFrame , when focused frame is...

Fix for Selection and showing context menu in the IFrame , when focused frame is subframe.

[Version] common
[Title] Context Menu not shown when do selectAll in IFrame.
[BinType] N/A
[Customer] HQ
[Issue#] DCM-2417
[Problem] Context Menu not shown when do selectAll in IFrame.
[Cause] In TextSelection::showContextMenu we always take ViewPort as MainFrame, not as FocusedFrame.
[Solution] Condition added so that when we ask to show the ContextMenu we will take view port as FocusedFrame in case SubFrame is selected.
[Team] WebCoreSupport
[Developer] m.gurnaney@samsung.com
[Request] N/A
[Horizontal expansion] N/A
[SCMRequest] NA

Change-Id: Ia67e11e0f701c788d9dee0f98f8199b5aab759c5