Add error handling to batch script (#10007)

bin/flutter.bat

@@ -80,9 +80,9 @@ GOTO :after_subroutine
   :do_sdk_update_and_snapshot
     ECHO Checking Dart SDK version...
     CALL PowerShell.exe -ExecutionPolicy Bypass -Command "& '%FLUTTER_ROOT%/bin/internal/update_dart_sdk.ps1'"
-    SET exit_code=%ERRORLEVEL%
-    IF %exit_code% NEQ 0 (
-      ECHO Error: Unable to update Dart SDK. Retrying... Press Ctrl+C to abort.
+    IF "%ERRORLEVEL%" NEQ "0" (
+      ECHO Error: Unable to update Dart SDK. Retrying...
+      timeout /t 5 /nobreak
       GOTO :do_sdk_update_and_snapshot
     )
 
@@ -104,11 +104,24 @@ GOTO :after_subroutine
         SET PUB_ENVIRONMENT=%PUB_ENVIRONMENT%:flutter_bot
       :not_on_bot
       SET PUB_ENVIRONMENT=%PUB_ENVIRONMENT%:flutter_install
+      :retry_pub_upgrade
       CALL "%pub%" upgrade --verbosity=error --no-packages-dir
+      IF "%ERRORLEVEL%" NEQ "0" (
+        ECHO Error: Unable to 'pub upgrade' flutter tool. Retrying...
+        timeout /t 5 /nobreak
+        GOTO :retry_pub_upgrade
+      )
     ENDLOCAL
 
     POPD
+
+    :retry_dart_snapshot
     CALL "%dart%" --snapshot="%snapshot_path%" --packages="%flutter_tools_dir%\.packages" "%script_path%"
+    IF "%ERRORLEVEL%" NEQ "0" (
+      ECHO Error: Unable to create dart snapshot for flutter tool. Retrying...
+      timeout /t 5 /nobreak
+      GOTO :retry_dart_snapshot
+    )
     >"%stamp_path%" ECHO %revision%
 
   REM Exit Subroutine
@@ -120,8 +133,13 @@ CALL "%dart%" %FLUTTER_TOOL_ARGS% "%snapshot_path%" %*
 SET exit_code=%ERRORLEVEL%
 
 REM The VM exits with code 253 if the snapshot version is out-of-date.
-IF /I "%exit_code%" EQU "253" (
+IF "%exit_code%" EQU "253" (
   CALL "%dart%" --snapshot="%snapshot_path%" --packages="%flutter_tools_dir%\.packages" "%script_path%"
+  SET exit_code=%ERRORLEVEL%
+  IF "%exit_code%" EQU "253" (
+    ECHO Error: Unable to create dart snapshot for flutter tool.
+    EXIT /B %exit_code%
+  )
   CALL "%dart%" %FLUTTER_TOOL_ARGS% "%snapshot_path%" %*
   SET exit_code=%ERRORLEVEL%
 )