Change error message to not use imperative tone

Change-Id: I605bf097b80495dd627f0b25490d28fca8bc2e70
Reviewed-on: https://dart-review.googlesource.com/60423
Reviewed-by: Peter von der Ahé <ahe@google.com>
Commit-Queue: Jens Johansen <jensj@google.com>
diff --git a/pkg/front_end/lib/src/fasta/fasta_codes_generated.dart b/pkg/front_end/lib/src/fasta/fasta_codes_generated.dart
index a7e68a5..a76cf2f 100644
--- a/pkg/front_end/lib/src/fasta/fasta_codes_generated.dart
+++ b/pkg/front_end/lib/src/fasta/fasta_codes_generated.dart
@@ -2839,7 +2839,7 @@
             string)> templateInitializeFromDillNotSelfContained = const Template<
         Message Function(String string)>(
     messageTemplate:
-        r"""Tried to initialize from a previous compilation (#string), but the file was not self-contained. This might be a bug, please report at http://dartbug.com/new.""",
+        r"""Tried to initialize from a previous compilation (#string), but the file was not self-contained. This might be a bug. The Dart team would greatly appreciate if you would take a moment to report this problem at http://dartbug.com/new.""",
     withArguments: _withArgumentsInitializeFromDillNotSelfContained);
 
 // DO NOT EDIT. THIS FILE IS GENERATED. SEE TOP OF FILE.
@@ -2854,7 +2854,7 @@
 Message _withArgumentsInitializeFromDillNotSelfContained(String string) {
   return new Message(codeInitializeFromDillNotSelfContained,
       message:
-          """Tried to initialize from a previous compilation (${string}), but the file was not self-contained. This might be a bug, please report at http://dartbug.com/new.""",
+          """Tried to initialize from a previous compilation (${string}), but the file was not self-contained. This might be a bug. The Dart team would greatly appreciate if you would take a moment to report this problem at http://dartbug.com/new.""",
       arguments: {'string': string});
 }
 
@@ -2866,7 +2866,7 @@
             string2)> templateInitializeFromDillUnknownProblem = const Template<
         Message Function(String string, String string2)>(
     messageTemplate:
-        r"""Tried to initialize from a previous compilation (#string), but couldn't. This might be a bug, please report at http://dartbug.com/new. Error message was '#string2'.""",
+        r"""Tried to initialize from a previous compilation (#string), but couldn't. Error message was '#string2'. This might be a bug. The Dart team would greatly appreciate if you would take a moment to report this problem at http://dartbug.com/new.""",
     withArguments: _withArgumentsInitializeFromDillUnknownProblem);
 
 // DO NOT EDIT. THIS FILE IS GENERATED. SEE TOP OF FILE.
@@ -2882,7 +2882,7 @@
     String string, String string2) {
   return new Message(codeInitializeFromDillUnknownProblem,
       message:
-          """Tried to initialize from a previous compilation (${string}), but couldn't. This might be a bug, please report at http://dartbug.com/new. Error message was '${string2}'.""",
+          """Tried to initialize from a previous compilation (${string}), but couldn't. Error message was '${string2}'. This might be a bug. The Dart team would greatly appreciate if you would take a moment to report this problem at http://dartbug.com/new.""",
       arguments: {'string': string, 'string2': string2});
 }
 
diff --git a/pkg/front_end/messages.yaml b/pkg/front_end/messages.yaml
index a58be2d..989fd27 100644
--- a/pkg/front_end/messages.yaml
+++ b/pkg/front_end/messages.yaml
@@ -2283,13 +2283,13 @@
   severity: IGNORED
 
 InitializeFromDillNotSelfContained:
-  template: "Tried to initialize from a previous compilation (#string), but the file was not self-contained. This might be a bug, please report at http://dartbug.com/new."
+  template: "Tried to initialize from a previous compilation (#string), but the file was not self-contained. This might be a bug. The Dart team would greatly appreciate if you would take a moment to report this problem at http://dartbug.com/new."
   severity: WARNING
   frontendInternal: true
   external: test/incremental_load_from_invalid_dill_test.dart
 
 InitializeFromDillUnknownProblem:
-  template: "Tried to initialize from a previous compilation (#string), but couldn't. This might be a bug, please report at http://dartbug.com/new. Error message was '#string2'."
+  template: "Tried to initialize from a previous compilation (#string), but couldn't. Error message was '#string2'. This might be a bug. The Dart team would greatly appreciate if you would take a moment to report this problem at http://dartbug.com/new."
   severity: WARNING
   frontendInternal: true
   external: test/incremental_load_from_invalid_dill_test.dart