[Extensions] Enable promise support on the storage API

This CL changes over the json schema to use the new returns_async format
to define callbacks, enabling promise support on those APIs.

Bug: 328932
Change-Id: I6b93bf1977582ff5a104820728ad891bd2a329e5
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2514965Reviewed-by: Devlin <rdevlin.cronin@chromium.org>
Commit-Queue: Tim Judkins <tjudkins@chromium.org>
Cr-Commit-Position: refs/heads/master@{#826845}

extensions/common/api/storage.json

@@ -51,21 +51,20 @@
                 ],
                 "description": "A single key to get, list of keys to get, or a dictionary specifying default values (see description of the object).  An empty list or object will return an empty result object.  Pass in <code>null</code> to get the entire contents of storage.",
                 "optional": true
-              },
-              {
-                "name": "callback",
-                "type": "function",
-                "description": "Callback with storage items, or on failure (in which case $(ref:runtime.lastError) will be set).",
-                "parameters": [
-                  {
-                    "name": "items",
-                    "type": "object",
-                    "additionalProperties": { "type": "any" },
-                    "description": "Object with items in their key-value mappings."
-                  }
-                ]
               }
-            ]
+            ],
+            "returns_async": {
+              "name": "callback",
+              "description": "Callback with storage items, or on failure (in which case $(ref:runtime.lastError) will be set).",
+              "parameters": [
+                {
+                  "name": "items",
+                  "type": "object",
+                  "additionalProperties": { "type": "any" },
+                  "description": "Object with items in their key-value mappings."
+                }
+              ]
+            }
           },
           {
             "name": "getBytesInUse",
@@ -80,20 +79,19 @@
                 ],
                 "description": "A single key or list of keys to get the total usage for. An empty list will return 0. Pass in <code>null</code> to get the total usage of all of storage.",
                 "optional": true
-              },
-              {
-                "name": "callback",
-                "type": "function",
-                "description": "Callback with the amount of space being used by storage, or on failure (in which case $(ref:runtime.lastError) will be set).",
-                "parameters": [
-                  {
-                    "name": "bytesInUse",
-                    "type": "integer",
-                    "description": "Amount of space being used in storage, in bytes."
-                  }
-                ]
               }
-            ]
+            ],
+            "returns_async": {
+              "name": "callback",
+              "description": "Callback with the amount of space being used by storage, or on failure (in which case $(ref:runtime.lastError) will be set).",
+              "parameters": [
+                {
+                  "name": "bytesInUse",
+                  "type": "integer",
+                  "description": "Amount of space being used in storage, in bytes."
+                }
+              ]
+            }
           },
           {
             "name": "set",
@@ -106,15 +104,14 @@
                 "additionalProperties": { "type": "any", "preserveNull": true },
                 "preserveNull": true,
                 "description": "<p>An object which gives each key/value pair to update storage with. Any other key/value pairs in storage will not be affected.</p><p>Primitive values such as numbers will serialize as expected. Values with a <code>typeof</code> <code>\"object\"</code> and <code>\"function\"</code> will typically serialize to <code>{}</code>, with the exception of <code>Array</code> (serializes as expected), <code>Date</code>, and <code>Regex</code> (serialize using their <code>String</code> representation).</p>"
-              },
-              {
-                "name": "callback",
-                "type": "function",
-                "description": "Callback on success, or on failure (in which case $(ref:runtime.lastError) will be set).",
-                "parameters": [],
-                "optional": true
               }
-            ]
+            ],
+            "returns_async": {
+              "name": "callback",
+              "description": "Callback on success, or on failure (in which case $(ref:runtime.lastError) will be set).",
+              "parameters": [],
+              "optional": true
+            }
           },
           {
             "name": "remove",
@@ -128,29 +125,26 @@
                   {"type": "array", "items": {"type": "string"}}
                 ],
                 "description": "A single key or a list of keys for items to remove."
-              },
-              {
-                "name": "callback",
-                "type": "function",
-                "description": "Callback on success, or on failure (in which case $(ref:runtime.lastError) will be set).",
-                "parameters": [],
-                "optional": true
               }
-            ]
+            ],
+            "returns_async": {
+              "name": "callback",
+              "description": "Callback on success, or on failure (in which case $(ref:runtime.lastError) will be set).",
+              "parameters": [],
+              "optional": true
+            }
           },
           {
             "name": "clear",
             "type": "function",
             "description": "Removes all items from storage.",
-            "parameters": [
-              {
-                "name": "callback",
-                "type": "function",
-                "description": "Callback on success, or on failure (in which case $(ref:runtime.lastError) will be set).",
-                "parameters": [],
-                "optional": true
-              }
-            ]
+            "parameters": [],
+            "returns_async":  {
+              "name": "callback",
+              "description": "Callback on success, or on failure (in which case $(ref:runtime.lastError) will be set).",
+              "parameters": [],
+              "optional": true
+            }
           }
         ],
         "events": [