JSON completion provider doesn't work without triggering characters.

test/playground.generated/extending-language-services-completion-provider-example.html

@@ -63,6 +63,7 @@ function createDependencyProposals() {
 
 
 monaco.languages.registerCompletionItemProvider('json', {
+    triggerCharacters: ['\"'],
     provideCompletionItems: function(model, position) {
         // find out if we are completing a property in the 'dependencies' object.
         var textUntilPosition = model.getValueInRange({startLineNumber: 1, startColumn: 1, endLineNumber: position.lineNumber, endColumn: position.column});

website/playground/new-samples/extending-language-services/completion-provider-example/sample.js

@@ -25,6 +25,7 @@ function createDependencyProposals() {
 
 
 monaco.languages.registerCompletionItemProvider('json', {
+    triggerCharacters: ['\"'],
     provideCompletionItems: function(model, position) {
         // find out if we are completing a property in the 'dependencies' object.
         var textUntilPosition = model.getValueInRange({startLineNumber: 1, startColumn: 1, endLineNumber: position.lineNumber, endColumn: position.column});