[Fuchsia] Use the "new_parts" section from the SDK manifest.

Update logic in gen_build_defs.py to match the SDK manifest data format
transition.

Bug: 951021
Change-Id: Ifaf5599e5cdecc9b32a6e285f3ca8ba36e9c48f8
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1562759Reviewed-by: Fabrice de Gans-Riberi <fdegans@chromium.org>
Commit-Queue: Kevin Marshall <kmarshall@chromium.org>
Cr-Commit-Position: refs/heads/master@{#649728}

third_party/fuchsia-sdk/gen_build_defs.py

@@ -187,12 +187,10 @@ def ConvertSdkManifests():
   with open(build_output_path, 'w') as buildfile:
     buildfile.write(_GENERATED_PREAMBLE)
 
-    for next_part in toplevel_meta['parts']:
-      parsed = json.load(open(os.path.join(sdk_base_dir, next_part)))
-      if 'type' not in parsed:
-        raise Exception("Couldn't find 'type' node in %s." % next_part)
+    for part in toplevel_meta['new_parts']:
+      parsed = json.load(open(os.path.join(sdk_base_dir, part['meta'])))
 
-      convert_function = _CONVERSION_FUNCTION_MAP.get(parsed['type'])
+      convert_function = _CONVERSION_FUNCTION_MAP.get(part['type'])
       if convert_function is None:
         raise Exception('Unexpected SDK artifact type %s in %s.' %
                         (parsed['type'], next_part))