func replaceLinePrefixCommentsWithBlankLine(src []byte) {
	for {
		i := bytes.Index(src, linePrefix)
		if i < 0 {
			break  
		}
		if i == 0 || src[i-1] == '\n' {
			for i < len(src) && src[i] != '\n' {
				src[i] = ' '
				i++
			}
		} else {
			i += len(linePrefix)
		}
		src = src[i:]
	}
}
This function replaces source lines starting with "//line " with a blank line.
It does this irrespective of whether the line is truly a line comment or not;
e.g., the line may be inside a string, or a /*-style comment; however that is
rather unlikely (proper testing would require a full Go scan which we want to
avoid for performance).
package godoc
import (
	"bytes"
	"go/ast"
	"go/parser"
	"go/token"
	pathpkg "path"
	"golang.org/x/tools/godoc/vfs"
)
var linePrefix = []byte("//line ")