Exclude engine sources from framework Dart analyzer checks (#35)

diff --git a/analysis_options.yaml b/analysis_options.yaml
index e3b1d6f..3541eac 100644
--- a/analysis_options.yaml
+++ b/analysis_options.yaml
@@ -29,6 +29,7 @@
     - "bin/cache/**"
       # Ignore protoc generated files
     - "dev/conductor/lib/proto/*"
+    - "engine/**"
 
 linter:
   rules:
diff --git a/dev/bots/analyze.dart b/dev/bots/analyze.dart
index 49a4e1f..9f371f6 100644
--- a/dev/bots/analyze.dart
+++ b/dev/bots/analyze.dart
@@ -1866,6 +1866,7 @@
   assert(filenames.last.isEmpty); // git ls-files gives a trailing blank 0x00
   filenames.removeLast();
   return filenames
+      .where((String filename) => !filename.startsWith('engine/'))
       .map<File>((String filename) => File(path.join(workingDirectory, filename)))
       .toList();
 }