refactor(change_detection): remove abstractions intended for multiple implementations

The new observer feature gives us a better model for plugging in custom methods of watching fields.
The original detector abstraction turned out to be incorrect. This commit removes the now
unnecessary abstractions which were originally intended as an extensibility point.

Author: EisenbergEffect

src/ast.js

@@ -1,7 +1,3 @@
-import {
-  WatchRecord
-} from './change_detection';
-
 import {
   _Handler,
   _ConstantHandler,
@@ -108,7 +104,7 @@ export class CollectionAST extends AST {
   }
 }
 
-class _ConstantWatchRecord extends WatchRecord {
+class _ConstantWatchRecord {
   constructor(watchGroup, expression, currentValue) {
     this.currentValue = currentValue;
     this.handler = new _ConstantHandler(watchGroup, expression, currentValue);
@@ -141,4 +137,4 @@ class _ConstantWatchRecord extends WatchRecord {
   get nextChange() {
     return null;
   }
-}
+}

src/change_detection.js

@@ -1,12 +1,3 @@
-import {
-  ChangeDetector,
-  ChangeDetectorGroup,
-  ChangeRecord,
-  MapChangeRecord,
-  MapKeyValue,
-  CollectionChangeRecord,
-  CollectionChangeItem
-} from './change_detection';
 /**
  * these cannot currently be defined in the DirtyCheckingRecord class itself,
  * unfortunately. They've been moved outside and de-const-ified for this
@@ -15,6 +6,7 @@ import {
 var _MODE_NAMES = [
   'MARKER', 'IDENT', 'REFLECT', 'GETTER', 'MAP[]', 'ITERABLE', 'MAP'
 ];
+
 var _MODE_MARKER_ = 0;
 var _MODE_IDENTITY_ = 1;
 var _MODE_REFLECT_ = 2;
@@ -34,7 +26,7 @@ export class GetterCache {
   }
 }
 
-export class DirtyCheckingChangeDetectorGroup extends ChangeDetector {
+export class DirtyCheckingChangeDetectorGroup {
   constructor(parent, cache) {
     this._parent = parent;
     this._getterCache = cache;
@@ -286,7 +278,7 @@ class ChangeIterator {
   }
 }
 
-class DirtyCheckingRecord extends ChangeRecord {
+class DirtyCheckingRecord {
   constructor(group, object, fieldName, getter, handler) {
     this._group = group;
     this._getter = getter;
@@ -341,12 +333,12 @@ class DirtyCheckingRecord extends ChangeRecord {
           if (this._mode !== _MODE_ITERABLE_) {
             // Last one was collection as well, don't reset state.
             this._mode = _MODE_ITERABLE_;
-            this.currentValue = new _CollectionChangeRecord();
+            this.currentValue = new CollectionChangeRecord();
           }
         } else if (this._mode !== _MODE_MAP_) {
           // Last one was collection as well, don't reset state.
           this._mode = _MODE_MAP_;
-          this.currentValue = new _MapChangeRecord();
+          this.currentValue = new MapChangeRecord();
         }
       } else {
         this._mode = _MODE_IDENTITY_;
@@ -439,7 +431,8 @@ class DirtyCheckingRecord extends ChangeRecord {
     return `${_MODE_NAMES[this._mode]}[${this.field}]{${hashCode}}`;
   }
 }
-class _MapChangeRecord extends MapChangeRecord {
+
+export class MapChangeRecord {
   constructor() {
     this._records = {}; // WeakMap perhaps?
     this._map = {};
@@ -668,7 +661,8 @@ class _MapChangeRecord extends MapChangeRecord {
     }
   }
 }
-class KeyValueRecord extends MapKeyValue {
+
+class KeyValueRecord {
   constructor(key) {
     this._key = key;
     this._previousValue = this._currentValue = null;
@@ -702,7 +696,8 @@ class KeyValueRecord extends MapKeyValue {
           : `${this._key}[${this._previousValue} -> ${this._currentValue}]`;
   }
 }
-class _CollectionChangeRecord extends CollectionChangeRecord {
+
+export class CollectionChangeRecord {
   constructor() {
     this._iterable = null;
     this._items = new DuplicateMap();
@@ -827,7 +822,7 @@ class _CollectionChangeRecord extends CollectionChangeRecord {
     // assert(isDirty == false);
   }
   /**
-   * A [_CollectionChangeRecord] is considered dirty if it has additions, moves
+   * A [CollectionChangeRecord] is considered dirty if it has additions, moves
    * or removals.
    */
   get isDirty() {
@@ -1087,7 +1082,8 @@ class _CollectionChangeRecord extends CollectionChangeRecord {
            "removals: " + removals.join(', ') + "\n";
   }
 }
-class ItemRecord extends CollectionChangeItem {
+
+class ItemRecord {
   constructor(item) {
     this.item = item;
     this.previousIndex = this.currentIndex = null;
@@ -1114,6 +1110,7 @@ class ItemRecord extends CollectionChangeItem {
       : `${this.item}[${this.previousIndex} -> ${this.currentIndex}]`;
   }
 }
+
 class _DuplicateItemRecordList {
   constructor() {
     this.head = this.tail = null;
@@ -1184,6 +1181,7 @@ class _DuplicateItemRecordList {
     return this.head === null;
   }
 }
+
 class DuplicateMap {
   constructor() {
     // For an identical behaviour to the Dart implementation, a Map or WeakMap is required. However,
@@ -1217,4 +1215,4 @@ class DuplicateMap {
   clear() {
     this._map.clear();
   }
-}
+}

src/dirty_checking.js

@@ -2,7 +2,6 @@
 /* jshint ignore:start */
 // TODO: JsHint right now fails for this code!
 export * from './ast';
-export * from './change_detection';
 export * from './dirty_checking';
 export * from './watch_group';
 /* jshint ignore:end */

src/index.js

@@ -29,4 +29,4 @@ export class Watch {
     _WatchList._remove(handler, this);
     handler.release();
   }
-}
+}

src/watch.js

@@ -2,10 +2,6 @@ import {
   AST
 } from './ast';
 
-import {
-  WatchRecord
-} from './change_detection';
-
 import {
   _LinkedList,
   _LinkedListItem,

src/watch_group.js

@@ -338,4 +338,4 @@ function methodInvoke(object, method, args) {
       return object[method].apply(object, args || __no_args__);
     }
   }
-}
+}

src/watch_record.js

@@ -9,13 +9,10 @@ import {
 } from '../src/ast';
 
 import {
+  GetterCache,
+  DirtyCheckingChangeDetector,
   CollectionChangeRecord,
   MapChangeRecord
-} from '../src/change_detection';
-
-import {
-  GetterCache,
-  DirtyCheckingChangeDetector
 } from '../src/dirty_checking';
 
 import {