Fix remaining warnings.

lib/compiler/implementation/ssa/nodes.dart

 // Copyright (c) 2011, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 interface HVisitor<R> {
   R visitAdd(HAdd node);
   R visitBitAnd(HBitAnd node);
   R visitBitNot(HBitNot node);
   R visitBitOr(HBitOr node);
   R visitBitXor(HBitXor node);
@@ skipping 604 matching lines @@
   void assignCommonDominator(HBasicBlock predecessor) {
     assert(isClosed());
     if (dominator === null) {
       // If this basic block doesn't have a dominator yet we use the
       // given predecessor as the dominator.
       predecessor.addDominatedBlock(this);
     } else if (predecessor.dominator !== null) {
       // If the predecessor has a dominator and this basic block has a
       // dominator, we find a common parent in the dominator tree and
       // use that as the dominator.
-      HBasicBlock first = dominator;
-      HBasicBlock second = predecessor;
-      while (first !== second) {
-        if (first.id > second.id) {
-          first = first.dominator;
+      HBasicBlock block0 = dominator;
+      HBasicBlock block1 = predecessor;
+      while (block0 !== block1) {
+        if (block0.id > block1.id) {
+          block0 = block0.dominator;
         } else {
-          second = second.dominator;
+          block1 = block1.dominator;
         }
-        assert(first !== null && second !== null);
+        assert(block0 !== null && block1 !== null);
       }
-      if (dominator !== first) {
+      if (dominator !== block0) {
         dominator.removeDominatedBlock(this);
-        first.addDominatedBlock(this);
+        block0.addDominatedBlock(this);
       }
     }
   }
 
   void forEachPhi(void f(HPhi phi)) {
     HPhi current = phis.first;
     while (current !== null) {
       f(current);
       current = current.next;
     }
@@ skipping 1578 matching lines @@
 class HIfBlockInformation {
   final HIf branch;
   final SubGraph thenGraph;
   final SubGraph elseGraph;
   final HBasicBlock joinBlock;
   HIfBlockInformation(this.branch,
                       this.thenGraph,
                       this.elseGraph,
                       this.joinBlock);
 }