add some more logging information to help diagnose the 'method not found' errors (flutter#4125)

Author: devoncarew

src/io/flutter/inspector/EvalOnDartLibrary.java

@@ -183,7 +183,7 @@ public <T extends Obj> CompletableFuture<T> getObjHelper(ObjRef instance, Inspec
         getIsolateId(), instance.getId(), new GetObjectConsumer() {
           @Override
           public void onError(RPCError error) {
-            future.completeExceptionally(new RuntimeException(error.toString()));
+            future.completeExceptionally(new RuntimeException("RPCError calling getObject: " + error.toString()));
           }
 
           @Override
@@ -193,7 +193,7 @@ public void received(Obj response) {
 
           @Override
           public void received(Sentinel response) {
-            future.completeExceptionally(new RuntimeException(response.toString()));
+            future.completeExceptionally(new RuntimeException("Sentinel calling getObject: " + response.toString()));
           }
         }
       );
@@ -254,13 +254,13 @@ public void received(Isolate response) {
       }
 
       @Override
-      public void received(Sentinel response) {
-        libraryRef.completeExceptionally(new RuntimeException(response.toString()));
+      public void onError(RPCError error) {
+        libraryRef.completeExceptionally(new RuntimeException("RPCError calling getIsolate:" + error.toString()));
       }
 
       @Override
-      public void onError(RPCError error) {
-        libraryRef.completeExceptionally(new RuntimeException(error.toString()));
+      public void received(Sentinel response) {
+        libraryRef.completeExceptionally(new RuntimeException("Sentinel calling getIsolate:" + response.toString()));
       }
     });
   }

src/io/flutter/inspector/InspectorService.java

@@ -379,12 +379,6 @@ private CompletableFuture<JsonElement> invokeServiceExtensionHelper(String metho
     vmService.callServiceExtension(
       getInspectorLibrary().getIsolateId(), ServiceExtensions.inspectorPrefix + methodName, params,
       new ServiceExtensionConsumer() {
-
-        @Override
-        public void onError(RPCError error) {
-          ret.completeExceptionally(new RuntimeException(error.getMessage()));
-        }
-
         @Override
         public void received(JsonObject object) {
           if (object == null) {
@@ -394,6 +388,11 @@ public void received(JsonObject object) {
             ret.complete(object.get("result"));
           }
         }
+
+        @Override
+        public void onError(RPCError error) {
+          ret.completeExceptionally(new RuntimeException("RPCError calling " + methodName + ": " + error.getMessage()));
+        }
       }
     );
     return ret;