Replace identical definitions of hashCode() in all subtypes of `Val…

…ueType` with a base class definition.

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=201957447

src/com/google/javascript/rhino/jstype/BooleanType.java

@@ -112,9 +112,4 @@ public BooleanLiteralSet getPossibleToBooleanOutcomes() {
   public <T> T visit(Visitor<T> visitor) {
     return visitor.caseBooleanType();
   }
-
-  @Override
-  public int hashCode() {
-    return System.identityHashCode(this);
-  }
 }

src/com/google/javascript/rhino/jstype/NullType.java

@@ -118,9 +118,4 @@ public BooleanLiteralSet getPossibleToBooleanOutcomes() {
   public <T> T visit(Visitor<T> visitor) {
     return visitor.caseNullType();
   }
-
-  @Override
-  public int hashCode() {
-    return System.identityHashCode(this);
-  }
 }

src/com/google/javascript/rhino/jstype/NumberType.java

@@ -111,9 +111,4 @@ public <T> T visit(Visitor<T> visitor) {
   public JSType autoboxesTo() {
     return getNativeType(JSTypeNative.NUMBER_OBJECT_TYPE);
   }
-
-  @Override
-  public int hashCode() {
-    return System.identityHashCode(this);
-  }
 }

src/com/google/javascript/rhino/jstype/StringType.java

@@ -111,9 +111,4 @@ public BooleanLiteralSet getPossibleToBooleanOutcomes() {
   public <T> T visit(Visitor<T> visitor) {
     return visitor.caseStringType();
   }
-
-  @Override
-  public int hashCode() {
-    return System.identityHashCode(this);
-  }
 }

src/com/google/javascript/rhino/jstype/SymbolType.java

@@ -118,9 +118,4 @@ public BooleanLiteralSet getPossibleToBooleanOutcomes() {
   public <T> T visit(Visitor<T> visitor) {
     return visitor.caseSymbolType();
   }
-
-  @Override
-  public int hashCode() {
-    return System.identityHashCode(this);
-  }
 }

src/com/google/javascript/rhino/jstype/ValueType.java

@@ -75,4 +75,9 @@ public HasPropertyKind getPropertyKind(String propertyName, boolean autobox) {
       return super.getPropertyKind(propertyName, autobox);
     }
   }
+
+  @Override
+  public final int hashCode() {
+    return System.identityHashCode(this);
+  }
 }

src/com/google/javascript/rhino/jstype/VoidType.java

@@ -119,9 +119,4 @@ public BooleanLiteralSet getPossibleToBooleanOutcomes() {
   public <T> T visit(Visitor<T> visitor) {
     return visitor.caseVoidType();
   }
-
-  @Override
-  public int hashCode() {
-    return System.identityHashCode(this);
-  }
 }