diagnose_bloat.py: respect the --no-goma option

Right now use_goma will be set to true if you have a ~/goma directory
on your system, not respecting any --no-goma option. I think it should
be the opposite: if you omit --no-goma, but don't have a ~/goma
directory, use_goma gets set to false.

Change-Id: I023ed84b121f9456be13e2bf5974f271dd8c8661
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1775580Reviewed-by: Andrew Grieve <agrieve@chromium.org>
Commit-Queue: Matthew Denton <mpdenton@chromium.org>
Cr-Commit-Position: refs/heads/master@{#691537}

tools/binary_size/diagnose_bloat.py

@@ -290,7 +290,7 @@ class _BuildHelper(object):
 
   def _SetDefaults(self):
     has_goma_dir = os.path.exists(os.path.join(os.path.expanduser('~'), 'goma'))
-    self.use_goma = self.use_goma or has_goma_dir
+    self.use_goma = self.use_goma and has_goma_dir
     self.max_load_average = (self.max_load_average or
                              str(multiprocessing.cpu_count()))