Implement webview.captureVisibleRegion()

extensions/common/api/_api_features.json

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 // This features file defines extension APIs implemented under src/extensions.
 // See extensions/common/features/* to understand this file, in particular
 // feature.h, simple_feature.h, and base_feature_provider.h.
 //
 // Note that specifying "web_page", "blessed_web_page", or "all" as a context
 // type will require manually updating chrome/renderer/resources/dispatcher.cc.
@@ skipping 442 matching lines @@
   }, {
     "internal": true,
     "channel": "dev",
     "contexts": ["webui"],
     "matches": [
       "chrome://chrome-signin/*",
       "chrome://media-router/*",
       "chrome://oobe/*"
     ]
   }],
+  "webViewExperimentalInternal": [{
+    "internal": true,
+    "channel": "dev",
+    "dependencies": ["permission:webview"],
+    "contexts": ["blessed_extension"]
+  }, {
+    "internal": true,

[Fady Samuel, 2016/01/20 21:50:22]

Drive by: I think we turn on experimental features for these WebUI pages but we
don't need to do that anymore, right? I don't want to expose experimental
<webview> features to WebUI if we don't need to.

[wjmaclean, 2016/01/20 21:58:13]

Done.

I'm happy enough to turn this off. Is there any danger of anything breaking when
we make the switch to non-experimental later? I can't think of any WebUI pages
that would be trying to use this particular API ...

+    "channel": "dev",
+    "contexts": ["webui"],
+    "matches": [
+      "chrome://chrome-signin/*",
+      "chrome://media-router/*",
+      "chrome://oobe/*"
+    ]
+  }],
   "webViewRequest": [{
     "dependencies": ["permission:webview"],
     "contexts": ["blessed_extension"]
   }, {
     "channel": "stable",
     "contexts": ["webui"],
     "matches": [
       "chrome://chrome-signin/*",
       "chrome://media-router/*",
       "chrome://oobe/*"
     ]
   }]
 }