Add source information to variable declarations in CPS.

This adds a source mapping to variable declarations in the beginning of a JS function, that points to the start of the corresponding Dart method:

foo: function() {
  var a, b;
  ^

maps to

foo() {
      ^

R=sigmund@google.com

Review URL: https://codereview.chromium.org/1772703002 .

pkg/compiler/lib/src/cps_ir/cps_ir_builder.dart

@@ -855,14 +855,16 @@ class IrBuilder {
   /// 1. Call [buildFunctionHeader].
   /// 2. Call `buildXXX` methods to build the body.
   /// 3. Call [makeFunctionDefinition] to finish.
-  ir.FunctionDefinition makeFunctionDefinition() {
+  ir.FunctionDefinition makeFunctionDefinition(
+      SourceInformation sourceInformation) {
     _ensureReturn();
     return new ir.FunctionDefinition(
         state.currentElement,
         state.thisParameter,
         state.functionParameters,
         state.returnContinuation,
-        root);
+        root,
+        sourceInformation: sourceInformation);
   }
 
   /// Create a invocation of the [method] on the super class where the call

pkg/compiler/lib/src/cps_ir/cps_ir_builder_task.dart

@@ -487,7 +487,8 @@ class IrBuilderVisitor extends ast.Visitor<ir.Primitive>
           sourceInformation:
           sourceInformationBuilder.buildImplicitReturn(constructor));
 
-      return irBuilder.makeFunctionDefinition();
+      return irBuilder.makeFunctionDefinition(
+          sourceInformationBuilder.buildVariableDeclaration());
     });
   }
 
@@ -738,7 +739,8 @@ class IrBuilderVisitor extends ast.Visitor<ir.Primitive>
       irBuilder.buildConstructorBodyHeader(getConstructorBodyParameters(body),
           getClosureScopeForNode(node));
       visit(node.body);
-      return irBuilder.makeFunctionDefinition();
+      return irBuilder.makeFunctionDefinition(
+          sourceInformationBuilder.buildVariableDeclaration());
     });
   }
 
@@ -781,7 +783,8 @@ class IrBuilderVisitor extends ast.Visitor<ir.Primitive>
           value: initialValue,
           sourceInformation:
           sourceInformationBuilder.buildReturn(sendSet.assignmentOperator));
-      return irBuilder.makeFunctionDefinition();
+      return irBuilder.makeFunctionDefinition(
+          sourceInformationBuilder.buildVariableDeclaration());
     });
   }
 
@@ -952,7 +955,8 @@ class IrBuilderVisitor extends ast.Visitor<ir.Primitive>
     } else {
       visit(node.body);
     }
-    return irBuilder.makeFunctionDefinition();
+    return irBuilder.makeFunctionDefinition(
+        sourceInformationBuilder.buildVariableDeclaration());
   }
 
   /// Builds the IR for creating an instance of the closure class corresponding

pkg/compiler/lib/src/cps_ir/cps_ir_nodes.dart

@@ -421,10 +421,17 @@ class FunctionDefinition extends InteriorNode {
   final Parameter receiverParameter;
   final List<Parameter> parameters;
   final Continuation returnContinuation;
+  final SourceInformation sourceInformation;
   Expression body;
 
-  FunctionDefinition(this.element, this.receiverParameter, this.parameters,
-      this.returnContinuation, this.body, {this.interceptorParameter});
+  FunctionDefinition(
+      this.element,
+      this.receiverParameter,
+      this.parameters,
+      this.returnContinuation,
+      this.body,
+      {this.interceptorParameter,
+       this.sourceInformation});
 
   accept(BlockVisitor visitor) => visitor.visitFunctionDefinition(this);
 
@@ -3040,7 +3047,8 @@ class CopyingVisitor extends TrampolineRecursiveVisitor {
     visit(node.body);
     FunctionDefinition copy = new FunctionDefinition(
         node.element, thisParameter, parameters, returnContinuation, _first,
-        interceptorParameter: interceptorParameter);
+        interceptorParameter: interceptorParameter,
+        sourceInformation: node.sourceInformation);
     _first = _current = null;
     return copy;
   }

pkg/compiler/lib/src/js_backend/codegen/codegen.dart

@@ -184,7 +184,8 @@ class CodeGenerator extends tree_ir.StatementVisitor
     if (jsVariables.length > 0) {
       // Would be nice to avoid inserting at the beginning of list.
       accumulator.insert(0, new js.ExpressionStatement(
-          new js.VariableDeclarationList(jsVariables)));
+          new js.VariableDeclarationList(jsVariables)
+              .withSourceInformation(function.sourceInformation)));
     }
     return new js.Fun(parameters, new js.Block(accumulator));
   }

pkg/compiler/lib/src/tree_ir/tree_ir_builder.dart

@@ -136,7 +136,8 @@ class Builder implements cps_ir.Visitor/*<NodeCallback|Node>*/ {
     returnContinuation = node.returnContinuation;
     phiTempVar = new Variable(node.element, null);
     Statement body = translateExpression(node.body);
-    return new FunctionDefinition(node.element, parameters, body);
+    return new FunctionDefinition(node.element, parameters, body,
+        sourceInformation: node.sourceInformation);
   }
 
   /// Returns a list of variables corresponding to the arguments to a method

pkg/compiler/lib/src/tree_ir/tree_ir_nodes.dart

@@ -654,10 +654,15 @@ class Unreachable extends Statement {
 class FunctionDefinition extends Node {
   final ExecutableElement element;
   final List<Variable> parameters;
+  final SourceInformation sourceInformation;
   Statement body;
 
   /// Creates a function definition and updates `writeCount` for [parameters].
-  FunctionDefinition(this.element, this.parameters, this.body) {
+  FunctionDefinition(
+      this.element,
+      this.parameters,
+      this.body,
+      {this.sourceInformation}) {
     for (Variable param in parameters) {
       param.writeCount++; // Being a parameter counts as a write.
     }