browser: make outlink gathering reusable

The outlink JS always executes its function, which means we can't safely
inject it if we want other JavaScript to be able to execute outlink
extraction. This updates it to instead expose a single outlink gathering
function, which is then explicitly  called by the outlink gatherer after
injecting the JS.

Author: mistydemeo

brozzler/browser.py

@@ -770,12 +770,26 @@ def extract_outlinks(self, timeout=60):
         self.logger.info("extracting outlinks")
         self.websock_thread.expect_result(self._command_id.peek())
         js = brozzler.jinja2_environment().get_template("extract-outlinks.js").render()
+        # This defines the method but doesn't extract outlinks yet
         msg_id = self.send_to_chrome(
-            method="Runtime.evaluate", params={"expression": js}
+            method="Runtime.evaluate",
+            suppress_logging=True,
+            params={"expression": js},
         )
         self._wait_for(
             lambda: self.websock_thread.received_result(msg_id), timeout=timeout
         )
+        self.websock_thread.expect_result(self._command_id.peek())
+
+        # Now we actually do outlink extraction
+        msg_id = self.send_to_chrome(
+            method="Runtime.evaluate",
+            params={"expression": "__brzl_outlinksString()"},
+        )
+        self._wait_for(
+            lambda: self.websock_thread.received_result(msg_id), timeout=timeout
+        )
+
         message = self.websock_thread.pop_result(msg_id)
         if (
             "result" in message

brozzler/js-templates/extract-outlinks.js

@@ -36,4 +36,6 @@ var __brzl_compileOutlinks = function(frame) {
 
     return outlinks;
 }
-__brzl_compileOutlinks(window).join('\n');
+var __brzl_outlinksString = function() {
+    return __brzl_compileOutlinks(window).join('\n');
+}