Simple fixes

runtime/vm/compiler.h

Index: runtime/vm/compiler.h
diff --git a/runtime/vm/compiler.h b/runtime/vm/compiler.h
index b7aaae1268985b3443bc6827432cb55f1cd58f85..4e2a5503ab1a3c610bc9cf2d39ccf050865d26ee 100644
--- a/runtime/vm/compiler.h
+++ b/runtime/vm/compiler.h
@@ -148,8 +148,7 @@ class Compiler : public AllStatic {
   // because the mutator thread changed the state (e.g., deoptimization,
   // deferred loading). The background compilation may retry to compile
   // the same function later.
-  static void AbortBackgroundCompilation(intptr_t deopt_id,
-                                         const char* msg = "");
+  static void AbortBackgroundCompilation(intptr_t deopt_id, const char* msg);
 };