RFC: Start refactoring to provide more than a single backend.

lib/compiler/implementation/ssa/optimize.dart

Index: lib/compiler/implementation/ssa/optimize.dart
diff --git a/lib/compiler/implementation/ssa/optimize.dart b/lib/compiler/implementation/ssa/optimize.dart
index 3e4edb64e01f0465c7e943a452204bde7b6eb501..095090074c68ae047c680355ecf91f312124cb82 100644
--- a/lib/compiler/implementation/ssa/optimize.dart
+++ b/lib/compiler/implementation/ssa/optimize.dart
@@ -333,7 +333,7 @@ class SsaConstantFolder extends HBaseVisitor implements OptimizationPhase {
 
   HInstruction visitRelational(HRelational node) {
     if (allUsersAreBoolifies(node)) {
-      Interceptors interceptors = compiler.builder.interceptors;
+      Interceptors interceptors = compiler.backend.builder.interceptors;
       HStatic oldTarget = node.target;
       Element boolifiedInterceptor =
           interceptors.getBoolifiedVersionOf(oldTarget.element);
@@ -403,7 +403,7 @@ class SsaConstantFolder extends HBaseVisitor implements OptimizationPhase {
     HInstruction newInstruction = handleIdentityCheck(node);
     if (newInstruction === null) {
       HStatic target = new HStatic(
-          compiler.builder.interceptors.getTripleEqualsInterceptor());
+          compiler.backend.builder.interceptors.getTripleEqualsInterceptor());
       node.block.addBefore(node, target);
       return new HIdentity(target, node.left, node.right);
     } else {
@@ -445,7 +445,7 @@ class SsaConstantFolder extends HBaseVisitor implements OptimizationPhase {
         return graph.addConstantBool(false);
       } else {
         // TODO(floitsch): cache interceptors.
-        Interceptors interceptors = compiler.builder.interceptors;
+        Interceptors interceptors = compiler.backend.builder.interceptors;
         Element equalsElement = interceptors.getEqualsInterceptor();
         // If we have a different element than [equalsElement], we
         // don't need to optimize this instruction to use another
@@ -587,7 +587,7 @@ class SsaCheckInserter extends HBaseVisitor implements OptimizationPhase {
   SsaCheckInserter(Compiler compiler) {
     SourceString lengthString = const SourceString('length');
     lengthInterceptor =
-        compiler.builder.interceptors.getStaticGetInterceptor(lengthString);
+        compiler.backend.builder.interceptors.getStaticGetInterceptor(lengthString);
   }
 
   void visitGraph(HGraph graph) {