refactor(change_detection): introduce enum ChangeDetectionStrategy

BREAKING CHANGE

Closes #2497

- change detection strategy type changes from string to ChangeDetectionStrategy
- CHECK_ONCE => ChangeDetectionStrategy.CheckOnce
- CHECKED => ChangeDetectionStrategy.Checked
- CHECK_ALWAYS => ChangeDetectionStrategy.CheckAlways
- DETACHED => ChangeDetectionStrategy.Detached
- ON_PUSH => ChangeDetectionStrategy.OnPush
- DEFAULT => ChangeDetectionStrategy.Default
- ON_PUSH_OBSERVE => ChangeDetectionStrategy.OnPushObserve

modules/examples/src/observable_models/cells.dart

@@ -5,7 +5,7 @@ import "package:angular2/src/core/facade/collection.dart"
 import "common.dart"
     show Company, Opportunity, Offering, Account, CustomDate, STATUS_LIST;
 import "package:angular2/directives.dart" show NgFor;
-import "package:angular2/angular2.dart" show Component, Directive, View;
+import "package:angular2/angular2.dart" show Component, Directive, View, ChangeDetectionStrategy;
 
 class HasStyle {
   int cellWidth;
@@ -17,7 +17,7 @@ class HasStyle {
 @Component(
     selector: "company-name",
     properties: const ["width: cell-width", "company"],
-    changeDetection: "ON_PUSH_OBSERVE"
+    changeDetection: ChangeDetectionStrategy.OnPushObserve
 )
 @View(
     directives: const [],
@@ -29,7 +29,7 @@ class CompanyNameComponent extends HasStyle {
 @Component(
     selector: "opportunity-name",
     properties: const ["width: cell-width", "opportunity"],
-    changeDetection: "ON_PUSH_OBSERVE"
+    changeDetection: ChangeDetectionStrategy.OnPushObserve
 )
 @View(
     directives: const [],
@@ -41,7 +41,7 @@ class OpportunityNameComponent extends HasStyle {
 @Component(
     selector: "offering-name",
     properties: const ["width: cell-width", "offering"],
-    changeDetection: "ON_PUSH_OBSERVE"
+    changeDetection: ChangeDetectionStrategy.OnPushObserve
 )
 @View(
     directives: const [],
@@ -59,7 +59,7 @@ class Stage {
 @Component(
     selector: "stage-buttons",
     properties: const ["width: cell-width", "offering"],
-    changeDetection: "ON_PUSH_OBSERVE"
+    changeDetection: ChangeDetectionStrategy.OnPushObserve
 )
 @View(directives: const [NgFor], template: '''
       <div [style.width.px]="cellWidth">
@@ -103,7 +103,7 @@ class StageButtonsComponent extends HasStyle {
 @Component(
     selector: "account-cell",
     properties: const ["width: cell-width", "account"],
-    changeDetection: "ON_PUSH_OBSERVE"
+    changeDetection: ChangeDetectionStrategy.OnPushObserve
 )
 @View(directives: const [], template: '''
       <div [style.width.px]="cellWidth">
@@ -117,7 +117,7 @@ class AccountCellComponent extends HasStyle {
 @Component(
     selector: "formatted-cell",
     properties: const ["width: cell-width", "value"],
-    changeDetection: "ON_PUSH_OBSERVE"
+    changeDetection: ChangeDetectionStrategy.OnPushObserve
 )
 @View(
     directives: const [],

modules/examples/src/observable_models/scroll_area.dart

@@ -2,7 +2,7 @@ library benchmarks.src.naive_infinite_scroll.scroll_area;
 
 import "package:angular2/src/core/facade/collection.dart" show ListWrapper;
 import "package:angular2/src/core/facade/math.dart" show Math;
-import "package:angular2/angular2.dart" show Component, Directive, View;
+import "package:angular2/angular2.dart" show Component, Directive, View, ChangeDetectionStrategy;
 import "common.dart"
     show
         Offering,
@@ -16,7 +16,7 @@ import "random_data.dart" show generateOfferings;
 import "scroll_item.dart" show ScrollItemComponent;
 import "package:angular2/directives.dart" show NgFor;
 
-@Component(selector: "scroll-area", changeDetection: "ON_PUSH_OBSERVE")
+@Component(selector: "scroll-area", changeDetection: ChangeDetectionStrategy.OnPushObserve)
 @View(directives: const [ScrollItemComponent, NgFor], template: '''
     <div>
         <div id="scrollDiv"

modules/examples/src/observable_models/scroll_item.dart

@@ -8,7 +8,7 @@ import "cells.dart"
         StageButtonsComponent,
         AccountCellComponent,
         FormattedCellComponent;
-import "package:angular2/angular2.dart" show Component, Directive, View;
+import "package:angular2/angular2.dart" show Component, Directive, View, ChangeDetectionStrategy;
 import "common.dart"
     show
         Offering,
@@ -25,7 +25,8 @@ import "common.dart"
         END_DATE_WIDTH,
         AAT_STATUS_WIDTH;
 
-@Component(selector: "scroll-item", properties: const ["offering"], changeDetection: "ON_PUSH_OBSERVE")
+@Component(selector: "scroll-item", properties: const ["offering"],
+  changeDetection: ChangeDetectionStrategy.OnPushObserve)
 @View(
     directives: const [
   CompanyNameComponent,