Avoid throwing an exception for hasTerminal

See dart-lang/test#1261

Throwing and immediately catching an exception has negative implications
for debugging and pausing on thrown exceptions. The exception is not
needed provided we duplicate a small bit of knowledge - that the
function to retrieve terminal size would return a non-list.

Change-Id: Ic92f7c0480d58963e857c699aa0251eedeb3e627
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/152922
Commit-Queue: Nate Bosch <[email protected]>
Auto-Submit: Nate Bosch <[email protected]>
Reviewed-by: Zichang Guo <[email protected]>

sdk/lib/_internal/vm/bin/stdio_patch.dart

@@ -126,15 +126,7 @@ class Stdin {
 @patch
 class Stdout {
   @patch
-  bool _hasTerminal(int fd) {
-    try {
-      _terminalSize(fd);
-      return true;
-    } catch (_) {
-      return false;
-    }
-  }
-
+  bool _hasTerminal(int fd) => _getTerminalSize(fd) is List;
   @patch
   int _terminalColumns(int fd) => _terminalSize(fd)[0];
   @patch