dart2js cps: Better fallthrough analysis and eliminate "return null".

tests/compiler/dart2js/js_backend_cps_ir_basic_test.dart

Index: tests/compiler/dart2js/js_backend_cps_ir_basic_test.dart
diff --git a/tests/compiler/dart2js/js_backend_cps_ir_basic_test.dart b/tests/compiler/dart2js/js_backend_cps_ir_basic_test.dart
index 264dc656ee072ed3b7f4f58a6f38b04540b66127..8ba0f45bcd0978a00420050cfcb4b9dd19f496d6 100644
--- a/tests/compiler/dart2js/js_backend_cps_ir_basic_test.dart
+++ b/tests/compiler/dart2js/js_backend_cps_ir_basic_test.dart
@@ -34,7 +34,6 @@ function() {
   P.print("(1)");
   P.print("(" + H.S(l) + ")");
   P.print("(" + H.S(m) + ")");
-  return null;
 }"""),
   const TestEntry("""
 foo(a, [b = "b"]) => b;
@@ -56,7 +55,6 @@ function() {
   V.bar(4, 5, "c");
   V.bar(6, "b", 7);
   V.bar(8, 9, 10);
-  return null;
 }"""),
   const TestEntry(
   """
@@ -83,7 +81,6 @@ function() {
   P.print(a);
   P.print(a);
   P.print(V.foo(b));
-  return null;
 }"""),
   const TestEntry(
   """
@@ -97,7 +94,6 @@ main() { return foo(); }
   const TestEntry("main() { return 42; }"),
   const TestEntry("main() { return; }", """
 function() {
-  return null;
 }"""),
   // Constructor invocation
   const TestEntry("""
@@ -108,7 +104,6 @@ main() {
 function() {
   P.print(P.LinkedHashSet_LinkedHashSet(null, null, null, null));
   P.print(P.LinkedHashSet_LinkedHashSet$from([1, 2, 3], null));
-  return null;
 }"""),
   // Call synthetic constructor.
   const TestEntry("""
@@ -123,7 +118,6 @@ main() {
 }""", r"""
 function() {
   P.print(P.DateTime$now().isBefore$1(P.DateTime$now()));
-  return null;
 }"""),
   // Static calls
   const TestEntry("""
@@ -132,7 +126,6 @@ main() { foo(); }
 """, r"""
 function() {
   V.foo();
-  return null;
 }"""),
   // Static getters
   const TestEntry("""
@@ -141,7 +134,6 @@ main() { print(foo); }
 """, r"""
 function() {
   P.print($.foo);
-  return null;
 }"""),
   const TestEntry("""
 get foo { print(42); }
@@ -149,7 +141,6 @@ main() { foo; }
 """, r"""
 function() {
   V.foo();
-  return null;
 }"""),
   // Static setters
   const TestEntry("""
@@ -160,7 +151,6 @@ function() {
   var v0 = 42;
   $.foo = v0;
   P.print(v0);
-  return null;
 }"""),
   const TestEntry("""
 set foo(x) { print(x); }
@@ -168,7 +158,6 @@ main() { foo = 42; }
 """, r"""
 function() {
   V.foo(42);
-  return null;
 }"""),
   // Assert
   const TestEntry("""
@@ -181,7 +170,6 @@ main() {
 }""", r"""
 function() {
   P.print("Done");
-  return null;
 }""")
 ];