Add "force inline" to internal annotations.

sdk/lib/_internal/compiler/js_lib/annotations.dart

Index: sdk/lib/_internal/compiler/js_lib/annotations.dart
diff --git a/sdk/lib/_internal/compiler/js_lib/annotations.dart b/sdk/lib/_internal/compiler/js_lib/annotations.dart
index 435221d7d262e1494ae42715048372d7fb61883f..c20098038129e57606faffa81d34859a523a1fba 100644
--- a/sdk/lib/_internal/compiler/js_lib/annotations.dart
+++ b/sdk/lib/_internal/compiler/js_lib/annotations.dart
@@ -22,6 +22,11 @@ class NoInline {
   const NoInline();
 }
 
+/// Tells the optimizing compiler to always inline the annotated method.
+class ForceInline {
+  const ForceInline();
+}
+
 // Ensures that the annotated method is represented internally using
 // IR nodes ([:value == true:]) or AST nodes ([:value == false:]).
 class IrRepresentation {