Add missing app permissions to media stream examples

For media_stream_audio example, add 'audioCapture' permission
For media_stream_video example, add 'videoCapture' permission

Missing these permissions will cause NavigatorUserMediaError

BUG=NONE
TEST=Build the app and load it into Chrome, you should see it's working.

Review URL: https://codereview.chromium.org/1374513002

Cr-Commit-Position: refs/heads/master@{#351120}

native_client_sdk/src/examples/api/media_stream_audio/example.dsc

@@ -16,5 +16,6 @@
   'NAME': 'media_stream_audio',
   'TITLE': 'MediaStream Audio',
   'GROUP': 'API',
-  'MIN_CHROME_VERSION': '35.0.0.0'
+  'MIN_CHROME_VERSION': '35.0.0.0',
+  'PERMISSIONS': ['audioCapture']
 }

native_client_sdk/src/examples/api/media_stream_video/example.dsc

@@ -16,8 +16,6 @@
   'NAME': 'media_stream_video',
   'TITLE': 'MediaStream Video',
   'GROUP': 'API',
-  'MIN_CHROME_VERSION': '35.0.0.0'
+  'MIN_CHROME_VERSION': '35.0.0.0',
+  'PERMISSIONS': ['videoCapture']
 }
-
-
-