much better reaction to opening/ closing details for a message after zooming

when the user taps show / hide details, scroll the webview up (show) or down (hide)
enough to compensate for the difference in header height.
fixes b/6319197 After pinch zooming, expanding the message details causes the message headers to jump
Change-Id: I64ced1b9a1d411fa0fa34a179f2ae629fc993088
3 files changed