Save/restore context when getting colors for a different state

Getting colors for a state different from the current state of the
corresponding widget without saving the context might trigger an
invalidation and a redraw. Because this was happening from the draw
function this resulted in a redraw loop and constant high CPU usage.

This could be triggered by selecting text or searching.

https://bugzilla.gnome.org/show_bug.cgi?id=755442

inspired by:
https://git.gnome.org/browse/evince/commit/?id=1987f04
linuxmint/xreader@e76a18d

libdocument/ev-document-misc.c

@@ -161,9 +161,11 @@ ev_document_misc_paint_one_page (cairo_t      *cr,
	GtkStateFlags state = gtk_widget_get_state_flags (widget);
        GdkRGBA fg, bg, shade_bg;

        gtk_style_context_save (context);
        gtk_style_context_get_background_color (context, state, &bg);
        gtk_style_context_get_color (context, state, &fg);
        gtk_style_context_get_color (context, state, &shade_bg);
        gtk_style_context_restore (context);
        shade_bg.alpha *= 0.5;

	gdk_cairo_set_source_rgba (cr, highlight ? &fg : &shade_bg);

libview/ev-view.c

@@ -3974,7 +3974,9 @@ get_cursor_color (GtkStyleContext *context,

		gdk_color_free (style_color);
	} else {
		gtk_style_context_save (context);
		gtk_style_context_get_color (context, GTK_STATE_FLAG_NORMAL, color);
		gtk_style_context_restore (context);
	}
}

@@ -5622,7 +5624,9 @@ draw_rubberband (EvView             *view,
	GdkRGBA          color;

	context = gtk_widget_get_style_context (GTK_WIDGET (view));
	gtk_style_context_save (context);
	gtk_style_context_get_background_color (context, GTK_STATE_FLAG_SELECTED, &color);
	gtk_style_context_restore (context);

	cairo_save (cr);

@@ -5811,12 +5815,15 @@ _ev_view_get_selection_colors (EvView  *view,

	state = gtk_widget_has_focus (widget) ? GTK_STATE_FLAG_SELECTED : GTK_STATE_FLAG_ACTIVE;
	context = gtk_widget_get_style_context (widget);
	gtk_style_context_save (context);

	if (bg_color)
		gtk_style_context_get_background_color (context, state, bg_color);

	if (fg_color)
		gtk_style_context_get_color (context, state, fg_color);

	gtk_style_context_restore (context);
}

static void