Generate merged trace config for use in the Android tree

This solves two problems:
1) Including > 1 .proto from the android tree is too complex due
   to the unusual way protoc handles relative include paths
   (foo/../external/proto.proto and external/proto.proto are
   considered distinct and then collide on multiple redefinitions).
2) We really don't want to expose the datasource-specific config to
   the rest of the tree. That causes just unnecessary mainteinance
   pain when trying to add new DataSourceConfig(s).

Bug: 71743564
Change-Id: I53f83ff69cc70a56f0d72383cac238100b554273
diff --git a/tools/gen_tracing_cpp_headers_from_protos.py b/tools/gen_tracing_cpp_headers_from_protos.py
index 49333da..ea6ce95 100755
--- a/tools/gen_tracing_cpp_headers_from_protos.py
+++ b/tools/gen_tracing_cpp_headers_from_protos.py
@@ -35,7 +35,7 @@
 
 def main():
   if not os.path.exists('.gn'):
-    print('This script mast be executed from the perfetto root directory')
+    print('This script must be executed from the perfetto root directory')
     return 1
   if len(sys.argv) < 2:
     print('Usage: %s out/xxx' % sys.argv[0])