Convert ExtensionMsg_ExecuteCode to LocalFrame mojom message

This CL converts ExtensionMsg_ExecuteCode and
ExtensionHostMsg_ExecuteCodeFinished to ExecuteCode()
in extensions::mojom::LocalFrame.

It cleans up extension_messages_param_traits.{cc,h} and the
unit test for the traits.

Bug: 1180858
Change-Id: I7a92bbbf9eaa89995a57c7b31f000d7303f3ffaf
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2752767
Commit-Queue: Julie Kim <[email protected]>
Reviewed-by: Dave Tapuska <[email protected]>
Reviewed-by: Reilly Grant <[email protected]>
Reviewed-by: Sam McNally <[email protected]>
Cr-Commit-Position: refs/heads/master@{#864179}
diff --git a/extensions/browser/script_executor.h b/extensions/browser/script_executor.h
index 0ad4f85..2c6cb7ea 100644
--- a/extensions/browser/script_executor.h
+++ b/extensions/browser/script_executor.h
@@ -40,7 +40,7 @@
 
 // Interface for executing extension content scripts (e.g. executeScript) as
 // described by the mojom::ExecuteCodeParams IPC, and notifying the
-// caller when responded with ExtensionHostMsg_ExecuteCodeFinished.
+// caller when responded with ExecuteCodeCallback.
 class ScriptExecutor {
  public:
   explicit ScriptExecutor(content::WebContents* web_contents);
@@ -129,9 +129,6 @@
   }
 
  private:
-  // The next value to use for request_id in mojom::ExecuteCodeParams.
-  int next_request_id_ = 0;
-
   content::WebContents* web_contents_;
 
   ScriptsExecutedNotification observer_;