dart2js: do typechecking even if suppressWarnings is on

this is necessary because the type of elements will not be
set unless the typechecker runs on the element. You need
the type to be set even when suppressWarnings is on because
in checked mode it is an error to declare a compiled constant
with inconsistent field types

Fixes #24653

BUG=
R=sigmund@google.com

Review URL: https://codereview.chromium.org/1411153005 .

pkg/compiler/lib/src/compiler.dart

@@ -1989,9 +1989,9 @@ class _CompilerResolution implements Resolution {
       assert(invariant(element, !element.isSynthesized || tree == null));
       ResolutionImpact resolutionImpact =
           compiler.resolver.resolve(element);
-      if (tree != null &&
-          !compiler.analyzeSignaturesOnly &&
-          !reporter.options.suppressWarnings) {
+      if (tree != null && !compiler.analyzeSignaturesOnly) {
+        // TODO(het): don't do this if suppressWarnings is on, currently we have
+        // to do it because the typechecker also sets types
         // Only analyze nodes with a corresponding [TreeElements].
         compiler.checker.check(element);
       }

pkg/compiler/lib/src/typechecker.dart

@@ -75,7 +75,7 @@ class TypeCheckerTask extends CompilerTask {
 }
 
 /**
- * Class used to report different warnings for differrent kinds of members.
+ * Class used to report different warnings for different kinds of members.
  */
 class MemberKind {
   static const MemberKind METHOD = const MemberKind("method");