Reapply change to update dart2js operator equals semantics to follow

lib/compiler/implementation/ssa/types.dart

Index: lib/compiler/implementation/ssa/types.dart
diff --git a/lib/compiler/implementation/ssa/types.dart b/lib/compiler/implementation/ssa/types.dart
index cac3924513ff5ad512b29ba7263a64d719cb9c52..b3fa03d48ddcdab6421071aa4baa950a78adcb7e 100644
--- a/lib/compiler/implementation/ssa/types.dart
+++ b/lib/compiler/implementation/ssa/types.dart
@@ -199,7 +199,7 @@ class HBooleanOrNullType extends HPrimitiveOrNullType {
     if (other.isUnknown()) return HType.BOOLEAN_OR_NULL;
     if (other.isBooleanOrNull()) return HType.BOOLEAN_OR_NULL;
     if (other.isBoolean()) return HType.BOOLEAN;
-    if (other.isNull()) return HType.NULL;
+    if (other.canBeNull()) return HType.NULL;
     return HType.CONFLICTING;
   }
 }
@@ -254,7 +254,7 @@ class HNumberOrNullType extends HPrimitiveOrNullType {
     if (other.isIntegerOrNull()) return HType.INTEGER_OR_NULL;
     if (other.isDoubleOrNull()) return HType.DOUBLE_OR_NULL;
     if (other.isNumberOrNull()) return HType.NUMBER_OR_NULL;
-    if (other.isNull()) return HType.NULL;
+    if (other.canBeNull()) return HType.NULL;
     return HType.CONFLICTING;
   }
 }
@@ -313,7 +313,7 @@ class HIntegerOrNullType extends HNumberOrNullType {
     if (other.isDoubleOrNull()) return HType.CONFLICTING;
     if (other.isNumber()) return HType.INTEGER;
     if (other.isNumberOrNull()) return HType.INTEGER_OR_NULL;
-    if (other.isNull()) return HType.NULL;
+    if (other.canBeNull()) return HType.NULL;
     return HType.CONFLICTING;
   }
 }
@@ -376,7 +376,7 @@ class HDoubleOrNullType extends HNumberOrNullType {
     if (other.isDoubleOrNull()) return HType.DOUBLE_OR_NULL;
     if (other.isNumber()) return HType.DOUBLE;
     if (other.isNumberOrNull()) return HType.DOUBLE_OR_NULL;
-    if (other.isNull()) return HType.NULL;
+    if (other.canBeNull()) return HType.NULL;
     return HType.CONFLICTING;
   }
 }
@@ -484,7 +484,7 @@ class HStringOrNullType extends HPrimitiveOrNullType {
     if (other is HBoundedPotentialPrimitiveString) {
       return other.canBeNull() ? HType.STRING_OR_NULL : HType.STRING;
     }
-    if (other.isNull()) return HType.NULL;
+    if (other.canBeNull()) return HType.NULL;
     return HType.CONFLICTING;
   }
 }
@@ -631,18 +631,17 @@ class HBoundedType extends HType {
       if (this.type === temp.type) {
         if (isExact()) {
           return this;
-        } else if (other.isExact()){
+        } else if (other.isExact()) {
           return other;
         } else if (canBeNull()) {
           return other;
         } else {
           return this;
         }
-      } else if (canBeNull() && other.canBeNull()) {
-        return HType.NULL;
       }
     }
     if (other.isUnknown()) return this;
+    if (other.canBeNull() && canBeNull()) return HType.NULL;
     return HType.CONFLICTING;
   }