Check for a passed-in type argument vector in the prolog of generic functions.

runtime/vm/native_arguments.h

Index: runtime/vm/native_arguments.h
diff --git a/runtime/vm/native_arguments.h b/runtime/vm/native_arguments.h
index 7100f9c58eb73e21a40a5b0b2c9a37af6382da1e..856c0437f582b01ef69d1b677492c27d9210d407 100644
--- a/runtime/vm/native_arguments.h
+++ b/runtime/vm/native_arguments.h
@@ -151,6 +151,7 @@ class NativeArguments {
 
   static intptr_t ParameterCountForResolution(const Function& function) {
     ASSERT(function.is_native());
+    ASSERT(!function.IsGeneric());                // Not supported.
     ASSERT(!function.IsGenerativeConstructor());  // Not supported.
     intptr_t count = function.NumParameters();
     if (function.is_static() && function.IsClosureFunction()) {
@@ -165,6 +166,7 @@ class NativeArguments {
 
   static int ComputeArgcTag(const Function& function) {
     ASSERT(function.is_native());
+    ASSERT(!function.IsGeneric());                // Not supported.
     ASSERT(!function.IsGenerativeConstructor());  // Not supported.
     int tag = ArgcBits::encode(function.NumParameters());
     int function_bits = 0;