[fuchsia] Fix an incorrect use of StringPiece

A StringPiece variable was used to store a returned value. Howevers,
StringPieces do not own the data they point to.

Bug: 1206010
Change-Id: I298acb855ff8c8e7f520146e6c531408b8c8e7df
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2875418
Commit-Queue: Fabrice de Gans-Riberi <fdegans@chromium.org>
Commit-Queue: David Dorwin <ddorwin@chromium.org>
Auto-Submit: Fabrice de Gans-Riberi <fdegans@chromium.org>
Reviewed-by: David Dorwin <ddorwin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#879513}
diff --git a/fuchsia/engine/browser/web_engine_devtools_controller.cc b/fuchsia/engine/browser/web_engine_devtools_controller.cc
index 2bbbb89..a55ca49 100644
--- a/fuchsia/engine/browser/web_engine_devtools_controller.cc
+++ b/fuchsia/engine/browser/web_engine_devtools_controller.cc
@@ -336,7 +336,7 @@
   if (command_line.HasSwitch(switches::kRemoteDebuggingPort)) {
     // Set up DevTools to listen on all network routes on the command-line
     // provided port.
-    base::StringPiece command_line_port_value =
+    std::string command_line_port_value =
         command_line.GetSwitchValueASCII(switches::kRemoteDebuggingPort);
     int parsed_port = 0;