Move all flags to CompilerOptions (first step to stop passing the compiler to

pkg/compiler/lib/src/resolution/signatures.dart

Index: pkg/compiler/lib/src/resolution/signatures.dart
diff --git a/pkg/compiler/lib/src/resolution/signatures.dart b/pkg/compiler/lib/src/resolution/signatures.dart
index df165a698898b86ffeb36c49b0046dea7d14f2f6..0fc9aac7dc86c83f8a0243f21f74f47e1b107960 100644
--- a/pkg/compiler/lib/src/resolution/signatures.dart
+++ b/pkg/compiler/lib/src/resolution/signatures.dart
@@ -342,7 +342,7 @@ class SignatureResolver extends MappingVisitor<FormalElementX> {
       returnType = element.enclosingClass.thisType;
       // Because there is no type annotation for the return type of
       // this element, we explicitly add one.
-      if (compiler.enableTypeAssertions) {
+      if (compiler.options.enableTypeAssertions) {
         registry.registerTypeUse(new TypeUse.checkedModeCheck(returnType));
       }
     } else {