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..3fba8029a138cea7767973b327f4e5441acf4c3c 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 +49,28 @@ PassRefPtr<Image> CSSPaintValue::image(const LayoutObject& layoutObject,
     m_generator = CSSPaintImageGenerator::create(
         name(), layoutObject.document(), m_paintImageGeneratorObserver);
 
-  return m_generator->paint(layoutObject, size, zoom);
+  if (!m_parsedInputArguments) {

[meade_UTC10, 2017/02/17 07:09:37]

If you make the type of m_parsedInputArguments just CSSStyleValueVector, you can
check on its length. But because of the issue I mentioned below, you might need
another way of determining whether you've parsed yet.

[renjieliu1, 2017/02/19 04:39:13]

I'm not sure if I should check the length since a function with no arguments
should be allowed. I'm making m_parsedInputArguments null again if parse failed.

+    m_parsedInputArguments = new CSSStyleValueVector();
+
+    // Parse arguments.
+    if (RuntimeEnabledFeatures::cssPaintAPIArgumentsEnabled()) {
+      const Vector<CSSSyntaxDescriptor>& inputArgumentTypes =
+          m_generator->inputArgumentTypes();
+      if (m_argumentVariableData.size() != inputArgumentTypes.size()) {

[meade_UTC10, 2017/02/17 07:09:37]

In these cases, is there a case where you bail early here, but can end up with
m_parsedInputArguments partially filled? You might need to clear
m_parsedInputArguments when you bail.

[renjieliu1, 2017/02/19 04:39:13]

thank you for the catch!

+        return nullptr;
+      }
+      for (size_t i = 0; i < m_argumentVariableData.size(); ++i) {
+        const CSSValue* parsedValue =
+            m_argumentVariableData[i]->parseForSyntax(inputArgumentTypes[i]);
+        if (!parsedValue)
+          return nullptr;

[meade_UTC10, 2017/02/17 07:09:37]

Likewise

[renjieliu1, 2017/02/19 04:39:13]

thank you!

+        m_parsedInputArguments->appendVector(
+            StyleValueFactory::cssValueToStyleValueVector(*parsedValue));
+      }
+    }
+  }
+
+  return m_generator->paint(layoutObject, size, zoom, m_parsedInputArguments);
 }
 
 void CSSPaintValue::Observer::paintImageGeneratorReady() {
@@ -73,6 +96,7 @@ DEFINE_TRACE_AFTER_DISPATCH(CSSPaintValue) {
   visitor->trace(m_name);
   visitor->trace(m_generator);
   visitor->trace(m_paintImageGeneratorObserver);
+  visitor->trace(m_parsedInputArguments);
   CSSImageGeneratorValue::traceAfterDispatch(visitor);
 }