supersize: Don't cluster by default. Make Diff() accept only SizeInfo.

tools/binary_size/libsupersize/describe.py

Index: tools/binary_size/libsupersize/describe.py
diff --git a/tools/binary_size/libsupersize/describe.py b/tools/binary_size/libsupersize/describe.py
index d6e4093b8883c1f2e2c8c59e0e4468621234bbc8..30a1db86c5357875b1d1953491c82f96a635724c 100644
--- a/tools/binary_size/libsupersize/describe.py
+++ b/tools/binary_size/libsupersize/describe.py
@@ -220,7 +220,6 @@ class Describer(object):
 
 def DescribeSizeInfoCoverage(size_info):
   """Yields lines describing how accurate |size_info| is."""
-  symbols = models.SymbolGroup(size_info.raw_symbols)
   for section in models.SECTION_TO_SECTION_NAME:
     if section == 'd':
       expected_size = sum(v for k, v in size_info.section_sizes.iteritems()
@@ -237,7 +236,7 @@ def DescribeSizeInfoCoverage(size_info):
       return template.format(section, size_percent, actual_size, len(group),
                              expected_size - actual_size)
 
-    in_section = symbols.WhereInSection(section)
+    in_section = size_info.symbols.WhereInSection(section)
     yield one_stat(in_section)
     yield '* Padding accounts for {} bytes ({:.1%})'.format(
         in_section.padding, float(in_section.padding) / in_section.size)