[CSSParser] Plumb streaming parser into at-rule handlers

This CL pushes stream-based parsing one level deeper in the stack for
at-rules. The most notable difference is that at-rule handler functions
are now responsible for tokenizing their own preludes and starting
block handling if needed.

Actual parsing for at-rule preludes is unchanged as of yet; the handler
functions generate token ranges on their own and parse them as before.
In future CLs we'll be able to convert each at-rule handler to make
full use of stream parsing.

Bug: 661854
Change-Id: Ia3345be73ab8cc9fce2537443e8a3ed9df017b96
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2208812Reviewed-by: Anders Hartvoll Ruud <andruud@chromium.org>
Commit-Queue: Kevin Babbitt <kbabbitt@microsoft.com>
Cr-Commit-Position: refs/heads/master@{#771906}

third_party/blink/renderer/core/css/parser/css_parser_impl.h

@@ -147,33 +147,18 @@ class CORE_EXPORT CSSParserImpl {
   StyleRuleBase* ConsumeAtRule(CSSParserTokenStream&, AllowedRulesType);
   StyleRuleBase* ConsumeQualifiedRule(CSSParserTokenStream&, AllowedRulesType);
 
-  static StyleRuleCharset* ConsumeCharsetRule(CSSParserTokenRange prelude);
+  static StyleRuleCharset* ConsumeCharsetRule(CSSParserTokenStream&);
   StyleRuleImport* ConsumeImportRule(AtomicString prelude_uri,
-                                     CSSParserTokenRange prelude,
-                                     const RangeOffset& prelude_offset);
-  StyleRuleNamespace* ConsumeNamespaceRule(CSSParserTokenRange prelude);
-  StyleRuleMedia* ConsumeMediaRule(CSSParserTokenRange prelude,
-                                   const RangeOffset& prelude_offset,
-                                   CSSParserTokenStream& block);
-  StyleRuleSupports* ConsumeSupportsRule(CSSParserTokenRange prelude,
-                                         const RangeOffset& prelude_offset,
-                                         CSSParserTokenStream& block);
-  StyleRuleViewport* ConsumeViewportRule(CSSParserTokenRange prelude,
-                                         const RangeOffset& prelude_offset,
-                                         CSSParserTokenStream& block);
-  StyleRuleFontFace* ConsumeFontFaceRule(CSSParserTokenRange prelude,
-                                         const RangeOffset& prelude_offset,
-                                         CSSParserTokenStream& block);
+                                     CSSParserTokenStream&);
+  StyleRuleNamespace* ConsumeNamespaceRule(CSSParserTokenStream&);
+  StyleRuleMedia* ConsumeMediaRule(CSSParserTokenStream&);
+  StyleRuleSupports* ConsumeSupportsRule(CSSParserTokenStream&);
+  StyleRuleViewport* ConsumeViewportRule(CSSParserTokenStream&);
+  StyleRuleFontFace* ConsumeFontFaceRule(CSSParserTokenStream&);
   StyleRuleKeyframes* ConsumeKeyframesRule(bool webkit_prefixed,
-                                           CSSParserTokenRange prelude,
-                                           const RangeOffset& prelude_offset,
-                                           CSSParserTokenStream& block);
-  StyleRulePage* ConsumePageRule(CSSParserTokenRange prelude,
-                                 const RangeOffset& prelude_offset,
-                                 CSSParserTokenStream& block);
-  StyleRuleProperty* ConsumePropertyRule(CSSParserTokenRange prelude,
-                                         const RangeOffset& prelude_offset,
-                                         CSSParserTokenStream& block);
+                                           CSSParserTokenStream&);
+  StyleRulePage* ConsumePageRule(CSSParserTokenStream&);
+  StyleRuleProperty* ConsumePropertyRule(CSSParserTokenStream&);
 
   StyleRuleKeyframe* ConsumeKeyframeStyleRule(CSSParserTokenRange prelude,
                                               const RangeOffset& prelude_offset,