Implement CSSPaintValue and add a layout test.

third_party/WebKit/Source/core/css/CSSPaintValue.cpp

Index: third_party/WebKit/Source/core/css/CSSPaintValue.cpp
diff --git a/third_party/WebKit/Source/core/css/CSSPaintValue.cpp b/third_party/WebKit/Source/core/css/CSSPaintValue.cpp
index d93ed2427d3ac01d91fb5ad2df69035ae8745ae8..82ccd3fdaa5cb396662826d137c7670a0c4b80a2 100644
--- a/third_party/WebKit/Source/core/css/CSSPaintValue.cpp
+++ b/third_party/WebKit/Source/core/css/CSSPaintValue.cpp
@@ -5,6 +5,8 @@
 #include "core/css/CSSPaintValue.h"
 
 #include "core/css/CSSCustomIdentValue.h"
+#include "core/css/CSSSyntaxDescriptor.h"
+#include "core/css/cssom/StyleValueFactory.h"
 #include "core/layout/LayoutObject.h"
 #include "platform/graphics/Image.h"
 #include "wtf/text/StringBuilder.h"
@@ -47,7 +49,44 @@ PassRefPtr<Image> CSSPaintValue::image(const LayoutObject& layoutObject,
     m_generator = CSSPaintImageGenerator::create(
         name(), layoutObject.document(), m_paintImageGeneratorObserver);
 
-  return m_generator->paint(layoutObject, size, zoom);
+  if (!parseInputArguments())
+    return nullptr;
+
+  return m_generator->paint(layoutObject, size, zoom, m_parsedInputArguments);
+}
+
+bool CSSPaintValue::parseInputArguments() {
+  if (m_inputArgumentsInvalid)
+    return false;
+
+  if (m_parsedInputArguments ||
+      !RuntimeEnabledFeatures::cssPaintAPIArgumentsEnabled())
+    return true;
+
+  if (!m_generator->isImageGeneratorReady())
+    return false;
+
+  const Vector<CSSSyntaxDescriptor>& inputArgumentTypes =
+      m_generator->inputArgumentTypes();
+  if (m_argumentVariableData.size() != inputArgumentTypes.size()) {
+    m_inputArgumentsInvalid = true;
+    return false;
+  }
+
+  m_parsedInputArguments = new CSSStyleValueVector();
+
+  for (size_t i = 0; i < m_argumentVariableData.size(); ++i) {
+    const CSSValue* parsedValue =
+        m_argumentVariableData[i]->parseForSyntax(inputArgumentTypes[i]);
+    if (!parsedValue) {
+      m_inputArgumentsInvalid = true;
+      m_parsedInputArguments = nullptr;
+      return false;
+    }
+    m_parsedInputArguments->appendVector(
+        StyleValueFactory::cssValueToStyleValueVector(*parsedValue));
+  }
+  return true;
 }
 
 void CSSPaintValue::Observer::paintImageGeneratorReady() {
@@ -73,6 +112,7 @@ DEFINE_TRACE_AFTER_DISPATCH(CSSPaintValue) {
   visitor->trace(m_name);
   visitor->trace(m_generator);
   visitor->trace(m_paintImageGeneratorObserver);
+  visitor->trace(m_parsedInputArguments);
   CSSImageGeneratorValue::traceAfterDispatch(visitor);
 }