Correctly indent the RHS of 'is' and 'as' expressions.

I'm surprised this has been wrong for so long.

R=kevmoo@google.com

Review URL: https://codereview.chromium.org//2521383002 .

CHANGELOG.md

@@ -1,6 +1,7 @@
 # 0.2.12-dev
 
 * Add support for assert() in constructor initializers.
+* Correctly indent the right-hand side of `is` and `as` expressions.
 
 # 0.2.11+1
 

lib/src/source_visitor.dart

@@ -159,11 +159,13 @@ class SourceVisitor implements AstVisitor {
 
   visitAsExpression(AsExpression node) {
     builder.startSpan();
+    builder.nestExpression();
     visit(node.expression);
     soloSplit();
     token(node.asOperator);
     space();
     visit(node.type);
+    builder.unnest();
     builder.endSpan();
   }
 
@@ -1240,12 +1242,14 @@ class SourceVisitor implements AstVisitor {
 
   visitIsExpression(IsExpression node) {
     builder.startSpan();
+    builder.nestExpression();
     visit(node.expression);
     soloSplit();
     token(node.isOperator);
     token(node.notOperator);
     space();
     visit(node.type);
+    builder.unnest();
     builder.endSpan();
   }
 

test/splitting/mixed.stmt

@@ -210,4 +210,16 @@ veryLongFunction() => longArgument + longArgument + longArgument;
 veryLongFunction() =>
     longArgument +
     longArgument +
-    longArgument;
+    longArgument;
+>>> initialize with as expression
+var longVariableName = identifierSoLongItWraps as SomeClassName;
+<<<
+var longVariableName =
+    identifierSoLongItWraps
+        as SomeClassName;
+>>> initialize with is expression
+var longVariableName = identifierSoLongItWraps is SomeClassName;
+<<<
+var longVariableName =
+    identifierSoLongItWraps
+        is SomeClassName;