Generate ninja files for api assembly and run ninja.

Change-Id: I003536e4ed4481acbdc041a6450106f8459d5978
diff --git a/orchestrator/ninja/ninja_syntax.py b/orchestrator/ninja/ninja_syntax.py
index 328c99c..df97b68 100644
--- a/orchestrator/ninja/ninja_syntax.py
+++ b/orchestrator/ninja/ninja_syntax.py
@@ -159,7 +159,7 @@
     self.chDir = chDir
 
   # TODO(spandandas): Update the syntax when aosp/2064612 lands
-  def stream() -> Iterator[str]:
+  def stream(self) -> Iterator[str]:
     yield f"subninja {self.subninja}"
 
 class Line(Node):