More changes to extension omnibox API for styles.

chrome/common/extensions/api/extension_api.json

 [
   {
     "namespace": "extension",
     "unprivileged": true,
     "types": [
       {
         "id": "MessageSender",
         "type": "object",
         "description": "An object containing information about the script context that sent a message or request.",
         "properties": {
@@ skipping 3910 matching lines @@
             "description": "The text that is put into the URL bar, and that is sent to the extension when the user chooses this entry."
           },
           "description": {
             "type": "string",
             "minLength": 1,
             "description": "The text that is displayed in the URL dropdown. Can optionally be stylized by the descriptionStyles parameter."
           },
           "descriptionStyles": {
             "type": "array",
             "optional": true,
-            "description": "An array of style objects, created using styleUrl, styleMatch, or styleDim. A style applies to the region of text specified by the style's starting offset and length. If there are any overlapping regions of text covered by multiple styles, the last-specified style will be applied to the overlapping region.",
+            "description": "An array of style objects, created using styleUrl, styleMatch, or styleDim. A style applies to the region of text specified by the style's starting offset and length. If there are any overlapping regions of text covered by multiple styles, they will be added together (e.g. 'match' + 'dim' will display a dimmed match). Not all style combinations will be visually distinct (e.g. 'url' + 'dim' may look identical to 'url').",
             "items": {
               "type": "object",
               "properties": {
                 "type": {"type": "string", "enum": ["url", "match", "dim"]},
                 "offset": {"type": "integer"},
-                "length": {"type": "integer"}
+                "length": {"type": "integer", "optional": true}
               }
             }
           }
         }
       }
     ],
     "functions": [
       {
         "name": "sendSuggestions",
         "nodoc": true,
         "type": "function",
         "description": "A callback passed to the onInputChanged event used for sending suggestions back to the browser.",
         "parameters": [
           {"type": "integer", "name": "requestId"},
           {
             "type": "array",
             "description": "Array of suggest results",
             "items": {
               "$ref": "SuggestResult"
             }
           }
         ]
       },
       {
         "name": "styleUrl",
         "type": "function",
-        "description": "Constructor for the descriptionStyles parameter of the suggest callback. This style designates a region of text matching a URL or filename.",
+        "description": "Constructor for the descriptionStyles parameter of the suggest callback. This style designates a region of text matching a URL or filename. A negative offset means the region will start at that many characters from the end of the description. If length is omitted, the region will apply for the rest of the description text.",
         "parameters": [
            {"type": "integer", "name": "offset", "minimum": 0},
-           {"type": "integer", "name": "length", "minimum": 1}
+           {"type": "integer", "name": "length", "minimum": 0, "optional": true}
         ]
       },
       {
         "name": "styleMatch",
         "type": "function",
-        "description": "Constructor for the descriptionStyles parameter of the suggest callback. This style designates a region of text matching what the user typed.",
+        "description": "Constructor for the descriptionStyles parameter of the suggest callback. This style designates a region of text matching what the user typed. A negative offset means the region will start at that many characters from the end of the description. If length is omitted, the region will apply for the rest of the description text.",
         "parameters": [
            {"type": "integer", "name": "offset", "minimum": 0},
-           {"type": "integer", "name": "length", "minimum": 1}
+           {"type": "integer", "name": "length", "minimum": 0, "optional": true}
         ]
       },
       {
         "name": "styleDim",
         "type": "function",
-        "description": "Constructor for the descriptionStyles parameter of the suggest callback. This style designates a region of dim helper text.",
+        "description": "Constructor for the descriptionStyles parameter of the suggest callback. This style designates a region of dim helper text. A negative offset means the region will start at that many characters from the end of the description. If length is omitted, the region will apply for the rest of the description text.",
         "parameters": [
            {"type": "integer", "name": "offset", "minimum": 0},
-           {"type": "integer", "name": "length", "minimum": 1}
+           {"type": "integer", "name": "length", "minimum": 0, "optional": true}
         ]
       }
     ],
     "events": [
       {
         "name": "onInputStarted",
         "type": "function",
         "description": "User has started a keyword input session by typing the extension's keyword. This is guaranteed to be sent exactly once per input session, and before any onInputChanged events.",
         "parameters": []
       },
@@ skipping 353 matching lines @@
                   "token": { "type": "string", "optional": true }
                 }
               }
             ]
           }
         ]
       }
     ]
   }
 ]