Optimize one-byte string's toUpperCase.

runtime/tests/vm/vm.status

 # Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 # for details. All rights reserved. Use of this source code is governed by a
 # BSD-style license that can be found in the LICENSE file.
 
 # These tests are expected to crash on all platforms.
 cc/ArrayNew_Overflow_Crash: Crash
 cc/AllocGeneric_Overflow: Crash
 cc/CodeImmutability: Crash
 
 cc/SNPrint_BadArgs: Skip
 
 # These tests are skipped because of the workaround to open issue 8594.
 cc/Debug_StackTraceDump1: Skip
 cc/Debug_StackTraceDump2: Skip
 
 # Flaky on buildbot. Issue 5133 and 10409.
 cc/Sleep: Pass, Fail
 
+cc/GenerateSource: Fail  # Issue 17857
+
 [ $arch == x64 ]
 cc/IsolateInterrupt: Skip
 
 # The following section refers to the dart vm tests which live under
 # runtime/tests/vm/dart.
 [ $system == windows ]
 cc/Dart2JSCompileAll: Skip
 cc/ExternalizeConstantStrings: Skip
 cc/ThreadInterrupterHigh: Skip
 cc/ThreadInterrupterMedium: Skip
@@ skipping 52 matching lines @@
 [ $compiler == none && ($runtime == drt || $runtime == dartium || $runtime == ContentShellOnAndroid) ]
 dart/mirrored_compilation_error_test: Skip # Can't pass needed VM flag
 
 [ $compiler == dartanalyzer || $compiler == dart2analyzer ]
 dart/optimized_stacktrace_test: StaticWarning
 
 dart/mirrored_compilation_error_test: CompileTimeError, OK # This test intentionally includes invalid method bodies.
 
 [ $compiler == none && $runtime == ContentShellOnAndroid ]
 dart/byte_array_test: RuntimeError # Issue 17612