[vm/kernel/bytecode] Minor fixes in bytecode generator

This CL contains 2 fixes:

* Instantiator type arguments for factory constructors are calculated
  using factory's type parameters and not class type parameters
  (as factory's body uses factory's type parameters in kernel AST)
  This improves reuse of instantiator type arguments in factory
  constructors (optimization).

* Result of _AssertionError::_throwNew call is dropped off the stack.
  Although control never returns from _throwNew, this fix is needed
  to maintain correct stack balance while compiling bytecode.

Change-Id: Ib781b0d790a89576ef62b768513663e7e509749c
Reviewed-on: https://dart-review.googlesource.com/69384
Reviewed-by: Zach Anderson <zra@google.com>
Commit-Queue: Alexander Markov <alexmarkov@google.com>

pkg/vm/lib/bytecode/gen_bytecode.dart

@@ -586,20 +586,21 @@ class BytecodeGenerator extends RecursiveVisitor<Null> {
     enclosingFunction = node.function;
     parentFunction = null;
     hasErrors = false;
-    if (node.isInstanceMember ||
-        node is Constructor ||
-        (node is Procedure && node.isFactory)) {
+    final isFactory = node is Procedure && node.isFactory;
+    if (node.isInstanceMember || node is Constructor || isFactory) {
       if (enclosingClass.typeParameters.isNotEmpty) {
         classTypeParameters =
             new Set<TypeParameter>.from(enclosingClass.typeParameters);
         // Treat type arguments of factory constructors as class
         // type parameters.
-        if (node is Procedure && node.isFactory) {
+        if (isFactory) {
           classTypeParameters.addAll(node.function.typeParameters);
         }
       }
       if (hasInstantiatorTypeArguments(enclosingClass)) {
-        final typeParameters = enclosingClass.typeParameters
+        final typeParameters = (isFactory
+                ? node.function.typeParameters
+                : enclosingClass.typeParameters)
             .map((p) => new TypeParameterType(p))
             .toList();
         instantiatorTypeArguments =
@@ -1797,6 +1798,7 @@ class BytecodeGenerator extends RecursiveVisitor<Null> {
     }
 
     _genStaticCall(throwNewAssertionError, new ConstantArgDesc(3), 3);
+    asm.emitDrop1();
 
     asm.bind(done);
   }

pkg/vm/testcases/bytecode/asserts.dart.expect

@@ -17,6 +17,7 @@ Bytecode {
   PushConstant         CP#2
   PushConstant         CP#4
   IndirectStaticCall   3, CP#3
+  Drop1
 L1:
   PushConstant         CP#2
   ReturnTOS
@@ -48,6 +49,7 @@ Bytecode {
   InstanceCall1        1, CP#4
   PushConstant         CP#6
   IndirectStaticCall   3, CP#5
+  Drop1
 L1:
   PushConstant         CP#7
   ReturnTOS

pkg/vm/testcases/bytecode/async.dart.expect

@@ -2498,6 +2498,7 @@ L3:
   PushConstant         CP#3
   PushConstant         CP#16
   IndirectStaticCall   3, CP#15
+  Drop1
 L2:
   Push                 r4
   PushConstant         CP#17