Eliminate constructor return types from summaries.

pkg/analyzer/lib/src/summary/format.dart

Index: pkg/analyzer/lib/src/summary/format.dart
diff --git a/pkg/analyzer/lib/src/summary/format.dart b/pkg/analyzer/lib/src/summary/format.dart
index c4fb417f34c8d680b1e1a6b10e2bdfbebfe8cb79..25e5649137766ec9baf989dc96c6ae1010151db6 100644
--- a/pkg/analyzer/lib/src/summary/format.dart
+++ b/pkg/analyzer/lib/src/summary/format.dart
@@ -997,8 +997,8 @@ class UnlinkedExecutable extends base.SummaryClass {
 
   /**
    * Declared return type of the executable.  Absent if the return type is
-   * `void`.  Note that when strong mode is enabled, the actual return type may
-   * be different due to type inference.
+   * `void` or the executable is a constructor.  Note that when strong mode is
+   * enabled, the actual return type may be different due to type inference.
    */
   UnlinkedTypeRef get returnType => _returnType;
 
@@ -1085,8 +1085,8 @@ class UnlinkedExecutableBuilder {
 
   /**
    * Declared return type of the executable.  Absent if the return type is
-   * `void`.  Note that when strong mode is enabled, the actual return type may
-   * be different due to type inference.
+   * `void` or the executable is a constructor.  Note that when strong mode is
+   * enabled, the actual return type may be different due to type inference.
    */
   void set returnType(UnlinkedTypeRefBuilder _value) {
     assert(!_finished);