[M42-Merge] fixup! Changed implementation of EWebView::GetSnapshot

[M42-Merge] fixup! Changed implementation of EWebView::GetSnapshot

MakeCurrent is missing in EWebView::GetSnapshot() where Evas_GL_API is used.
This results in error below inside EvasGL when EvasGL API is called.
"Unable to retrieve Current Engine"

Static allocation of quite large amount of memory caused crash.

Query for GL_IMPLEMENTATION_COLOR_READ_FORMAT returns GL_RGBA, so to use
GL_BGRA results in GL_INVALID_OPERATION error in the case of glReadPixels.

The functionality of EWebView::GetSnapshot was verified on both mobile (Note4)
and tv (XU3).

Original Commit: http://165.213.202.130/gerrit/#/c/83886/

Bug: http://107.108.218.239/bugzilla/show_bug.cgi?id=13517

Reviewed by: a1.gomes, dhyuna.ko, siba.samal, sns.park

Change-Id: Ie1dd9cf096e4fc92cde6e952f8c318a06da0e7f7
Signed-off-by: dhyuna.ko <dhyuna.ko@samsung.com>
Signed-off-by: venu.musham <venu.musham@samsung.com>