[LazyParseCSS] WIP Implement token discarding

third_party/WebKit/Source/core/css/parser/CSSLazyPropertyParserImpl.cpp

Index: third_party/WebKit/Source/core/css/parser/CSSLazyPropertyParserImpl.cpp
diff --git a/third_party/WebKit/Source/core/css/parser/CSSLazyPropertyParserImpl.cpp b/third_party/WebKit/Source/core/css/parser/CSSLazyPropertyParserImpl.cpp
index 7431d1176b3fe0d5ec14f158b6ee2b4f09a2244d..985d69b7b1cc46bf660b55d3272701c049b9f448 100644
--- a/third_party/WebKit/Source/core/css/parser/CSSLazyPropertyParserImpl.cpp
+++ b/third_party/WebKit/Source/core/css/parser/CSSLazyPropertyParserImpl.cpp
@@ -6,6 +6,7 @@
 
 #include "core/css/parser/CSSLazyParsingState.h"
 #include "core/css/parser/CSSParserImpl.h"
+#include "core/css/parser/CSSTokenizer.h"
 
 namespace blink {
 
@@ -16,10 +17,52 @@ CSSLazyPropertyParserImpl::CSSLazyPropertyParserImpl(CSSParserTokenRange block,
   size_t length = block.end() - block.begin();
   m_tokens.reserveCapacity(length);
   m_tokens.append(block.begin(), length);
+
+  // TEST:
+  discardTokensIfPossible();
+}
+
+CSSLazyPropertyParserImpl::~CSSLazyPropertyParserImpl() {}
+
+// If the first and last tokens have a string backing, generate a StringView
+// from their character offsets. Note that this assumes they share a backing
+// string! Be extremely careful that the first and last token do not point to a
+// string in the escaped string pool!
+void CSSLazyPropertyParserImpl::discardTokensIfPossible() {
+  CSSParserToken* begin = m_tokens.begin();
+  CSSParserToken* end = m_tokens.end() - 1;
+  if (!begin->hasStringBacking() || !end->hasStringBacking())
+    return;
+
+  StringView beginView = begin->value();
+  StringView endView = end->value();
+  if (m_lazyState->tokenBackingUsesEscapedString(beginView.bytes()) ||
+      m_lazyState->tokenBackingUsesEscapedString(endView.bytes()))
+    return;
+  if (beginView.is8Bit() && endView.is8Bit()) {
+    m_tokenView = StringView(
+        beginView.characters8(),
+        endView.characters8() - beginView.characters8() + endView.length());
+  } else if (!beginView.is8Bit() && !endView.is8Bit()) {
+    m_tokenView = StringView(
+        beginView.characters16(),
+        endView.characters16() - beginView.characters16() + endView.length());
+  } else {
+    NOTREACHED();
+  }
+  m_tokens.clear();
+}
+
+StylePropertySet* CSSLazyPropertyParserImpl::retokenizeAndParseProperties() {
+  CSSTokenizer tokenizer(m_tokenView.toString());
+  return CSSParserImpl::parseDeclarationListForLazyStyle(
+      tokenizer.tokenRange(), m_lazyState->context());
 }
 
 StylePropertySet* CSSLazyPropertyParserImpl::parseProperties() {
   m_lazyState->countRuleParsed();
+  if (m_tokens.isEmpty())
+    return retokenizeAndParseProperties();
   return CSSParserImpl::parseDeclarationListForLazyStyle(
       m_tokens, m_lazyState->context());
 }