Suppress our "pixel" test on mac since it diffs.

This involves bringing some of the suppressions file
mechanism into run_pixel_tests.py (making a common
module would be a nice follow-up)

R=thestig@chromium.org

Review URL: https://codereview.chromium.org/1032923002
diff --git a/testing/SUPPRESSIONS_mac b/testing/SUPPRESSIONS_mac
index b0ffc7d..3f41d7e 100644
--- a/testing/SUPPRESSIONS_mac
+++ b/testing/SUPPRESSIONS_mac
@@ -1,2 +1,3 @@
 # List of tests to be skipped on mac platforms, one per line.
 # Try to keep the file alphabetized.
+font_size.in
diff --git a/testing/tools/run_pixel_tests.py b/testing/tools/run_pixel_tests.py
index ef2c31e..0665718 100755
--- a/testing/tools/run_pixel_tests.py
+++ b/testing/tools/run_pixel_tests.py
@@ -15,6 +15,12 @@
 #   x_path - "path/to/a/b/c/x.ext"
 #   c_dir - "path/to/a/b/c"
 
+def extract_suppressions(filename):
+  with open(filename) as f:
+    suppressions = [y for y in [
+      x.split('#')[0].strip() for x in f.readlines()] if y]
+  return suppressions
+
 def generate_and_test(input_filename, source_dir, working_dir,
                       fixup_path, pdfium_test_path, pdfium_diff_path):
   input_root, _ = os.path.splitext(input_filename)
@@ -46,6 +52,16 @@
   return True
 
 def main():
+  if sys.platform.startswith('linux'):
+    os_name = 'linux'
+  elif sys.platform.startswith('win'):
+    os_name = 'win'
+  elif sys.platform.startswith('darwin'):
+    os_name = 'mac'
+  else:
+    print 'Confused, can not determine OS, aborting.'
+    return 1
+
   parser = optparse.OptionParser()
   parser.add_option('--build-dir', default=os.path.join('out', 'Debug'),
                     help='relative path from the base source directory')
@@ -94,12 +110,26 @@
   if not os.path.exists(working_dir):
     os.makedirs(working_dir)
 
+  suppression_list = extract_suppressions(
+    os.path.join(testing_dir, 'SUPPRESSIONS'))
+
+  platform_suppression_filename = 'SUPPRESSIONS_%s' % os_name
+  platform_suppression_list = extract_suppressions(
+    os.path.join(testing_dir, platform_suppression_filename))
+
   failures = []
   input_file_re = re.compile('^[a-zA-Z0-9_.]+[.]in$')
   for input_filename in os.listdir(source_dir):
     if input_file_re.match(input_filename):
       input_path = os.path.join(source_dir, input_filename)
       if os.path.isfile(input_path):
+        if input_filename in suppression_list:
+          print "Not running %s, found in SUPPRESSIONS file" % input_filename
+          continue
+        if input_filename in platform_suppression_list:
+          print ("Not running %s, found in %s file" %
+                 (input_filename, platform_suppression_filename))
+          continue
         if not generate_and_test(input_filename, source_dir, working_dir,
                                  fixup_path, pdfium_test_path, pdfium_diff_path):
           failures.append(input_path)