Check whether the plugin is disabled in OnIsInternalPluginRegisteredForMimeType().

chrome/common/render_messages.h

 // Copyright (c) 2012 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.
 
 // Multiply-included file, no traditional include guard.
 #include <stdint.h>
 #include <map>
 #include <set>
 #include <string>
 #include <vector>
@@ skipping 412 matching lines @@
 // about specific reasons why a plug-in can't be used, for example because it's
 // disabled.
 IPC_SYNC_MESSAGE_CONTROL4_1(ChromeViewHostMsg_GetPluginInfo,
                             int /* render_frame_id */,
                             GURL /* url */,
                             GURL /* top origin url */,
                             std::string /* mime_type */,
                             ChromeViewHostMsg_GetPluginInfo_Output /* output */)
 
 #if defined(ENABLE_PEPPER_CDMS)
-// Returns whether any internal plugin supporting |mime_type| is registered
+// Returns whether any internal plugin supporting |mime_type| is available.

[ddorwin, 2014/07/21 17:54:58]

Should we update these comments per my suggestions in the previous header?

[xhwang, 2014/07/21 18:16:42]

Done.

 // Does not determine whether the plugin can actually be instantiated
-// (e.g. whether it is allowed or has all its dependencies).
-// When the returned *|is_registered| is true, |additional_param_names| and
+// (e.g. whether it has all its dependencies).
+// When the returned *|is_available| is true, |additional_param_names| and
 // |additional_param_values| contain the name-value pairs, if any, specified
-// for the *first* plugin found that is registered for |mime_type|.
+// for the *first* non-disabled plugin found that is registered for |mime_type|.
 IPC_SYNC_MESSAGE_CONTROL1_3(
-    ChromeViewHostMsg_IsInternalPluginRegisteredForMimeType,
+    ChromeViewHostMsg_IsInternalPluginAvailableForMimeType,
     std::string /* mime_type */,
-    bool /* registered */,
+    bool /* available */,

[ddorwin, 2014/07/21 17:54:58]

nit: is_available?

[xhwang, 2014/07/21 18:16:42]

Done.

     std::vector<base::string16> /* additional_param_names */,
     std::vector<base::string16> /* additional_param_values */)
 #endif
 
 #if defined(ENABLE_PLUGIN_INSTALLATION)
 // Tells the browser to search for a plug-in that can handle the given MIME
 // type. The result will be sent asynchronously to the routing ID
 // |placeholder_id|.
 IPC_MESSAGE_ROUTED2(ChromeViewHostMsg_FindMissingPlugin,
                     int /* placeholder_id */,
@@ skipping 215 matching lines @@
 // process so that they can be assigned to an Instant renderer.
 IPC_MESSAGE_CONTROL2(ChromeViewMsg_SetSearchURLs,
                      std::vector<GURL> /* search_urls */,
                      GURL /* new_tab_page_url */)
 
 #if defined(ENABLE_PLUGINS)
 // Sent by the renderer to check if crash reporting is enabled.
 IPC_SYNC_MESSAGE_CONTROL0_1(ChromeViewHostMsg_IsCrashReportingEnabled,
                             bool /* enabled */)
 #endif