feat(change detect): Throw on attempts to use dehydrated detector

- Modify change detectors to `throw` when attempting to detect changes
  on a dehydrated detector.
- Modify `DynamicChagneDetector` to use `null` for the `context` of a
  dehydrated detector.

modules/angular2/src/change_detection/change_detection_jit_generator.dart

@@ -1,5 +1,11 @@
 library change_detectoin.change_detection_jit_generator;
 
+/// Placeholder JIT generator for Dart.
+/// Dart does not support `eval`, so JIT generation is not an option. Instead,
+/// the Dart transformer pre-generates these Change Detector classes and
+/// registers them with the system. See `PreGeneratedChangeDetection`,
+/// `PregenProtoChangeDetector`, and
+/// `src/transform/template_compiler/change_detector_codegen.dart` for details.
 class ChangeDetectorJITGenerator {
   ChangeDetectorJITGenerator(typeName, strategy, records, directiveMementos) {}
 

modules/angular2/src/change_detection/change_detection_jit_generator.ts

@@ -98,6 +98,9 @@ export class ChangeDetectorJITGenerator {
       ${this.typeName}.prototype = Object.create(${ABSTRACT_CHANGE_DETECTOR}.prototype);
 
       ${this.typeName}.prototype.detectChangesInRecords = function(throwOnChange) {
+        if (!this.hydrated()) {
+          ${UTIL}.throwDehydrated();
+        }
         ${this._genLocalDefinitions()}
         ${this._genChangeDefinitions()}
         var ${IS_CHANGED_LOCAL} = false;
@@ -131,7 +134,7 @@ export class ChangeDetectorJITGenerator {
       }
 
       ${this.typeName}.prototype.hydrated = function() {
-        return Boolean(${CONTEXT_ACCESSOR});
+        return ${CONTEXT_ACCESSOR} !== null;
       }
 
       return function(dispatcher, pipeRegistry) {

modules/angular2/src/change_detection/change_detection_util.ts

@@ -1,7 +1,7 @@
 import {isPresent, isBlank, BaseException, Type} from 'angular2/src/facade/lang';
 import {List, ListWrapper, MapWrapper, StringMapWrapper} from 'angular2/src/facade/collection';
 import {ProtoRecord} from './proto_record';
-import {ExpressionChangedAfterItHasBeenChecked} from './exceptions';
+import {DehydratedException, ExpressionChangedAfterItHasBeenChecked} from './exceptions';
 import {WrappedValue} from './pipes/pipe';
 import {CHECK_ALWAYS, CHECK_ONCE, CHECKED, DETACHED, ON_PUSH} from './constants';
 
@@ -127,6 +127,8 @@ export class ChangeDetectionUtil {
     throw new ExpressionChangedAfterItHasBeenChecked(proto, change);
   }
 
+  static throwDehydrated() { throw new DehydratedException(); }
+
   static changeDetectionMode(strategy: string) {
     return strategy == ON_PUSH ? CHECK_ONCE : CHECK_ALWAYS;
   }

modules/angular2/src/change_detection/dynamic_change_detector.ts

@@ -44,7 +44,8 @@ export class DynamicChangeDetector extends AbstractChangeDetector {
     this.prevContexts = ListWrapper.createFixedSize(protos.length + 1);
     this.changes = ListWrapper.createFixedSize(protos.length + 1);
 
-    ListWrapper.fill(this.values, uninitialized);
+    this.values[0] = null;
+    ListWrapper.fill(this.values, uninitialized, 1);
     ListWrapper.fill(this.pipes, null);
     ListWrapper.fill(this.prevContexts, uninitialized);
     ListWrapper.fill(this.changes, false);
@@ -60,7 +61,8 @@ export class DynamicChangeDetector extends AbstractChangeDetector {
 
   dehydrate() {
     this._destroyPipes();
-    ListWrapper.fill(this.values, uninitialized);
+    this.values[0] = null;
+    ListWrapper.fill(this.values, uninitialized, 1);
     ListWrapper.fill(this.changes, false);
     ListWrapper.fill(this.pipes, null);
     ListWrapper.fill(this.prevContexts, uninitialized);
@@ -75,9 +77,12 @@ export class DynamicChangeDetector extends AbstractChangeDetector {
     }
   }
 
-  hydrated(): boolean { return this.values[0] !== uninitialized; }
+  hydrated(): boolean { return this.values[0] !== null; }
 
   detectChangesInRecords(throwOnChange: boolean) {
+    if (!this.hydrated()) {
+      ChangeDetectionUtil.throwDehydrated();
+    }
     var protos: List<ProtoRecord> = this.protos;
 
     var changes = null;

modules/angular2/src/change_detection/exceptions.ts

@@ -27,4 +27,8 @@ export class ChangeDetectionError extends BaseException {
   }
 
   toString(): string { return this.message; }
-}
+}
+
+export class DehydratedException extends BaseException {
+  constructor() { super('Attempt to detect changes on a dehydrated detector.'); }
+}

modules/angular2/src/transform/template_compiler/change_detector_codegen.dart

@@ -113,6 +113,9 @@ class _CodegenState {
             this.$_DIRECTIVES_ACCESSOR) : super();
 
         void detectChangesInRecords(throwOnChange) {
+          if (!hydrated()) {
+            $_UTIL.throwDehydrated();
+          }
           ${_genLocalDefinitions()}
           ${_genChangeDefinitons()}
           var $_IS_CHANGED_LOCAL = false;
@@ -145,7 +148,7 @@ class _CodegenState {
           $_LOCALS_ACCESSOR = null;
         }
 
-        hydrated() => $_CONTEXT_ACCESSOR == null;
+        hydrated() => $_CONTEXT_ACCESSOR != null;
 
         static $_GEN_PREFIX.ProtoChangeDetector
             $PROTO_CHANGE_DETECTOR_FACTORY_METHOD(