Adds support for layout tests.

tools/testing/drt-trampoline.py

Index: tools/testing/drt-trampoline.py
diff --git a/tools/testing/drt-trampoline.py b/tools/testing/drt-trampoline.py
index fec2ab21d375c2acc24b11dc9cb26718f30e13c2..2c7b033e009e2aa0cc64013d483043f6fabd0b90 100644
--- a/tools/testing/drt-trampoline.py
+++ b/tools/testing/drt-trampoline.py
@@ -13,6 +13,7 @@ import subprocess
 import sys
 
 DART_FLAGS_PREFIX = '--dart-flags='
+OUT_EXPECTATION_PREFIX = '--out-expectation='
 
 def main(argv):
   drt_path = argv[1]
@@ -21,18 +22,72 @@ def main(argv):
   cmd = [drt_path]
 
   env = None
+  test_file = None
+  out_expected_file = None
+  is_png = False
+
+  # parse arguments, filtering out flags, and selecting the input test file
   for arg in command_line:
     if arg.startswith(DART_FLAGS_PREFIX):
       env = dict(os.environ.items())
       env['DART_FLAGS'] = arg[len(DART_FLAGS_PREFIX):]
+    elif arg.startswith(OUT_EXPECTATION_PREFIX):
+      out_expected_file = arg[len(OUT_EXPECTATION_PREFIX):]
+      if out_expected_file.endswith('.png'):
+        cmd.append('--pixel-tests')
+        cmd.append('--notree')
+        is_png = True
+      elif not out_expected_file.endswith('.txt'):
+        raise Exception(
+            'Bad file expectation (%s), ' % out_expected_file
+            + 'please specify either a .txt or a .png file')
+    elif arg.endswith('.html'):
+      test_file = arg
+      cmd.append(arg)
     else:
       cmd.append(arg)
 
-  p = subprocess.Popen(cmd, env=env)
+
+  p = subprocess.Popen(cmd, env=env, stdout=subprocess.PIPE)
   p.wait()
   if p.returncode != 0:
     raise Exception('Failed to run command. return code=%s' % p.returncode)
 
+  if out_expected_file:
+    # Compare output to the given expectation file.
+    output = None
+    expectation = None
+    with p.stdout as res:
+      if is_png:
+        # DRT prints the image to STDOUT, but includes 5 header lines.
+        for i in range(4): res.readline()
+      output = res.read()
+    if os.path.exists(out_expected_file):
+      with open(out_expected_file, 'r') as f:
+        expectation = f.read()
+    else:
+      # Instructions on how to create the expectation will be printed below
+      # (outout != expectation)
+      print 'File %s was not found' % out_expected_file
+      expectation = None
+
+    # Report test status using the format test.dart expects to see from DRT.
+    print 'Content-Type: text/plain'
+    if expectation == output:
+      print 'PASS'
+      print 'Expectation matches'
+    else:
+      # Generate a temporary file in the same place as the .html file:
+      out_file = test_file[:test_file.rfind('.html')] + out_expected_file[-4:]
+      with open(out_file, 'w') as f:
+        f.write(output)
+      print 'FAIL'
+      print 'Expectation didn\'t match. Update expectations by running:\n'
+      print 'cp %s %s\n' % (out_file, out_expected_file)
+    print '#EOF'
+  else:
+    # Pipe through the output for non-layout tests.
+    sys.stdout.write(p.stdout.read())
 
 if __name__ == '__main__':
   try: