[Presubmit] Make CSS checker ignore '@' inside of strings.

This fixes the bug where url('google_logo.png@2x') causes validation
failures.

BUG=408759
R=dbeam@chromium.org

Review URL: https://codereview.chromium.org/514403002

Cr-Commit-Position: refs/heads/master@{#293603}

chrome/browser/test_presubmit.py

@@ -455,15 +455,20 @@ class CssStyleGuideTest(SuperMoxTestBase):
     self.mox.StubOutWithMock(self.output_api, 'PresubmitPromptWarning',
                              use_mock_anything=True)
 
-    author_msg = ('Was the CSS checker useful? '
-                  'Send feedback or hate mail to dbeam@chromium.org.')
     self.output_api = self.mox.CreateMockAnything()
     self.mox.StubOutWithMock(self.output_api, 'PresubmitNotifyResult',
                              use_mock_anything=True)
-    self.output_api.PresubmitNotifyResult(author_msg).AndReturn(None)
+
+  def VerifyContentsIsValid(self, contents):
+    self.fake_file.NewContents().AndReturn(contents.splitlines())
+    self.mox.ReplayAll()
+    css_checker.CSSChecker(self.input_api, self.output_api).RunChecks()
 
   def VerifyContentsProducesOutput(self, contents, output):
     self.fake_file.NewContents().AndReturn(contents.splitlines())
+    author_msg = ('Was the CSS checker useful? '
+                  'Send feedback or hate mail to dbeam@chromium.org.')
+    self.output_api.PresubmitNotifyResult(author_msg).AndReturn(None)
     self.output_api.PresubmitPromptWarning(
         self.fake_file_name + ':\n' + output.strip()).AndReturn(None)
     self.mox.ReplayAll()
@@ -508,6 +513,24 @@ class CssStyleGuideTest(SuperMoxTestBase):
     z-index: 5;
     color: black;""")
 
+  def testCssStringWithAt(self):
+    self.VerifyContentsIsValid("""
+#logo {
+  background-image: url('images/google_logo.png@2x');
+}
+
+body.alternate-logo #logo {
+  -webkit-mask-image: url('images/google_logo.png@2x');
+  background: none;
+}
+
+.stuff1 {
+}
+
+.stuff2 {
+}
+      """)
+
   def testCssAlphaWithNonStandard(self):
     self.VerifyContentsProducesOutput("""
 div {

chrome/browser/web_dev_style/css_checker.py

@@ -33,9 +33,9 @@ class CSSChecker(object):
 
     def _remove_ats(s):
       at_reg = re.compile(r"""
-          @\w+.*?{    # @at-keyword selector junk {
-          (.*{.*?})+  # inner { curly } blocks, rules, and selector junk
-          .*?}        # stuff up to the first end curly }""",
+          @\w+[^'"]*?{  # @at-keyword selector junk {
+          (.*{.*?})+    # inner { curly } blocks, rules, and selector junk
+          .*?}          # stuff up to the first end curly }""",
           re.DOTALL | re.VERBOSE)
       return at_reg.sub('\\1', s)