Trap window.onerror by default.

Changes gwt.uncaughtexceptionhandler.windowonerror
to REPORT_IF_NO_HANDLER.
This is a good default for most GWT applications.
see: https://gwt-review.googlesource.com/c/gwt/+/18540

This re-rolls commit e1f1eb0a118d5413c78b93feaa2f3f7689a2b911

Change-Id: I4f2e9e923136356b48a306f36f4c05ff9c21fe92

user/src/com/google/gwt/core/Core.gwt.xml

diff --git a/user/src/com/google/gwt/core/Core.gwt.xml b/user/src/com/google/gwt/core/Core.gwt.xml
index 5fcc52b..5569fe4 100644
--- a/user/src/com/google/gwt/core/Core.gwt.xml
+++ b/user/src/com/google/gwt/core/Core.gwt.xml
@@ -92,7 +92,7 @@
      - Do not trap anything (legacy behavior) (IGNORE)
   -->
   <define-property name="gwt.uncaughtexceptionhandler.windowonerror" values="IGNORE, REPORT, REPORT_IF_NO_HANDLER" />
-  <set-property name="gwt.uncaughtexceptionhandler.windowonerror" value="IGNORE"/>
+  <set-property name="gwt.uncaughtexceptionhandler.windowonerror" value="REPORT_IF_NO_HANDLER"/>
 
   <!-- To support legacy logging flags -->
   <inherits name="com.google.gwt.logging.LogImpl"/>

user/test/com/google/gwt/core/WindowOnError.gwt.xml

diff --git a/user/test/com/google/gwt/core/WindowOnError.gwt.xml b/user/test/com/google/gwt/core/WindowOnError.gwt.xml
deleted file mode 100644
index 0f34c54..0000000
--- a/user/test/com/google/gwt/core/WindowOnError.gwt.xml
+++ /dev/null
@@ -1,18 +0,0 @@
-<!--                                                                        -->
-<!-- Copyright 2017 Google Inc.                                             -->
-<!-- Licensed under the Apache License, Version 2.0 (the "License"); you    -->
-<!-- may not use this file except in compliance with the License. You may   -->
-<!-- may obtain a copy of the License at                                    -->
-<!--                                                                        -->
-<!-- http://www.apache.org/licenses/LICENSE-2.0                             -->
-<!--                                                                        -->
-<!-- Unless required by applicable law or agreed to in writing, software    -->
-<!-- distributed under the License is distributed on an "AS IS" BASIS,      -->
-<!-- WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or        -->
-<!-- implied. License for the specific language governing permissions and   -->
-<!-- limitations under the License.                                         -->
-
-<module>
-  <inherits name="com.google.gwt.core.Core" />
-  <set-property name="gwt.uncaughtexceptionhander.windowonerror" value="REPORT_IF_NO_HANDLER"/>
-</module>

user/test/com/google/gwt/core/client/WindowOnErrorTest.java

diff --git a/user/test/com/google/gwt/core/client/WindowOnErrorTest.java b/user/test/com/google/gwt/core/client/WindowOnErrorTest.java
index 6752b84..ea4e305 100644
--- a/user/test/com/google/gwt/core/client/WindowOnErrorTest.java
+++ b/user/test/com/google/gwt/core/client/WindowOnErrorTest.java
@@ -27,7 +27,7 @@
 
   @Override
   public String getModuleName() {
-    return "com.google.gwt.core.WindowOnError";
+    return "com.google.gwt.core.Core";
   }
 
   @Override