Reapply "Refactor constant part." (r4958) with fixes.

frog/tests/leg/src/SsaPhiEliminatorTest.dart

Index: frog/tests/leg/src/SsaPhiEliminatorTest.dart
diff --git a/frog/tests/leg/src/SsaPhiEliminatorTest.dart b/frog/tests/leg/src/SsaPhiEliminatorTest.dart
index d17e0a3ed4ded98560d359f422fb5a7f67d1ce33..59b09e9c298dbb9ec525ffc604d3b92ad77cd33d 100644
--- a/frog/tests/leg/src/SsaPhiEliminatorTest.dart
+++ b/frog/tests/leg/src/SsaPhiEliminatorTest.dart
@@ -56,10 +56,10 @@ foo() {
 
 main() {
   String generated = compile(TEST_ONE, 'foo');
-  RegExp regexp = const RegExp("a = 2");
+  RegExp regexp = const RegExp(@"a = \(2\)");
   Expect.isTrue(regexp.hasMatch(generated));
 
-  regexp = const RegExp("a = 3");
+  regexp = const RegExp(@"a = \(3\)");
   Expect.isTrue(regexp.hasMatch(generated));
 
   regexp = const RegExp(@"print\$1\(a\)");
@@ -82,7 +82,7 @@ main() {
   Expect.isTrue(regexp.hasMatch(generated));
   // Check that a store just after the declaration of the local
   // only generates one instruction.
-  regexp = const RegExp("var val = 42");
+  regexp = const RegExp(@"var val = \(42\)");
   Expect.isTrue(regexp.hasMatch(generated));
 
   generated = compile(TEST_FOUR, 'foo');