Log unresolved URIs using 'logInformation', so don't send to IDE.

pkg/analyzer/lib/src/generated/source.dart

Index: pkg/analyzer/lib/src/generated/source.dart
diff --git a/pkg/analyzer/lib/src/generated/source.dart b/pkg/analyzer/lib/src/generated/source.dart
index 1a4751678597008be0e04437eaa118bd5e69fd35..a0b88a166bc5b9afd677ed8e2bd886da9acf6e1a 100644
--- a/pkg/analyzer/lib/src/generated/source.dart
+++ b/pkg/analyzer/lib/src/generated/source.dart
@@ -743,7 +743,7 @@ class SourceFactory {
     } catch (exception, stackTrace) {
       String containingFullName =
           containingSource != null ? containingSource.fullName : '<null>';
-      AnalysisEngine.instance.logger.logError(
+      AnalysisEngine.instance.logger.logInformation(
           "Could not resolve URI ($containedUri) relative to source ($containingFullName)",
           new CaughtException(exception, stackTrace));
       return null;