[test] Increase buffer for reading memory usage.

test/cctest/heap/test-mark-compact.cc

Index: test/cctest/heap/test-mark-compact.cc
diff --git a/test/cctest/heap/test-mark-compact.cc b/test/cctest/heap/test-mark-compact.cc
index d0f7f8274139ef092a0306e21aaa2062593069dd..7a636ef5a24813c69d1d5b9c914973df63dcb6f3 100644
--- a/test/cctest/heap/test-mark-compact.cc
+++ b/test/cctest/heap/test-mark-compact.cc
@@ -415,7 +415,7 @@ static intptr_t MemoryInUse() {
   int fd = open("/proc/self/maps", O_RDONLY);
   if (fd < 0) return -1;
 
-  const int kBufSize = 10000;
+  const int kBufSize = 20000;
   char buffer[kBufSize];
   ssize_t length = read(fd, buffer, kBufSize);
   intptr_t line_start = 0;