Update tabCapture API docs with browser action info.

chrome/browser/extensions/api/tab_capture/tab_capture_api.cc

Index: chrome/browser/extensions/api/tab_capture/tab_capture_api.cc
diff --git a/chrome/browser/extensions/api/tab_capture/tab_capture_api.cc b/chrome/browser/extensions/api/tab_capture/tab_capture_api.cc
index 07dec25ffdcdd6aa845640bea3d02014e5aa40ec..1a5d1c00d22114b2b274c418dc8d742086efb1eb 100644
--- a/chrome/browser/extensions/api/tab_capture/tab_capture_api.cc
+++ b/chrome/browser/extensions/api/tab_capture/tab_capture_api.cc
@@ -41,7 +41,8 @@ const char kFindingTabError[] = "Error finding tab to capture.";
 const char kNoAudioOrVideo[] = "Capture failed. No audio or video requested.";
 const char kPermissionError[] = "Tab Capture API flag is not enabled.";
 const char kGrantError[] =
-    "Capture of this tab must be granted by clicking on the extension icon.";
+    "Capture of this tab must be granted through a user action (see the "
+    "activeTab permission). Chrome pages cannot be captured.";
 
 // Keys/values for media stream constraints.
 const char kMediaStreamSource[] = "chromeMediaSource";