increase javac_filter line length limit to 2MB

Some javac wrappers output the entire list of java files being
compiled on a single line, which can be very large, set the maximum
buffer size to 2MB.

Test: pipe the grok build output through soong_javac_wrapper
Change-Id: Ib208461dca02ced4959433b7695ec760dc134468

cmd/javac_filter/javac_filter.go

@@ -54,6 +54,10 @@ func main() {
 
 func process(r io.Reader, w io.Writer) error {
 	scanner := bufio.NewScanner(r)
+	// Some javac wrappers output the entire list of java files being
+	// compiled on a single line, which can be very large, set the maximum
+	// buffer size to 2MB.
+	scanner.Buffer(nil, 2*1024*1024)
 	for scanner.Scan() {
 		processLine(w, scanner.Text())
 	}