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..b84bb4e69e737bf68d85eba723377c17cbe74df3 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 +49,31 @@ 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) {

[ikilpatrick, 2017/02/21 17:40:36]

This is unfortunately racy. You'll need to check if the generator is "ready" yet
before getting the inputArgumentsTypes from it.

It may make sense to make this into CSSPaintValue:paintImageGeneratorReady if
this code block doesn't depend on layoutObject, size, or zoom.

(This can happen if you use a css paint() function before the paint worklet has
loaded its script for example).

[renjieliu1, 2017/02/22 04:47:54]

thank you for the suggestion! I will keep the code inside CSSPaintValue::image
since it's easier to check whether m_generator is ready and parse the input
arguments.

+    m_parsedInputArguments = new CSSStyleValueVector();
+
+    // Parse arguments.
+    if (RuntimeEnabledFeatures::cssPaintAPIArgumentsEnabled()) {
+      const Vector<CSSSyntaxDescriptor>& inputArgumentTypes =
+          m_generator->inputArgumentTypes();
+      if (m_argumentVariableData.size() != inputArgumentTypes.size()) {
+        m_parsedInputArguments = nullptr;
+        return nullptr;
+      }
+      for (size_t i = 0; i < m_argumentVariableData.size(); ++i) {
+        const CSSValue* parsedValue =
+            m_argumentVariableData[i]->parseForSyntax(inputArgumentTypes[i]);
+        if (!parsedValue) {
+          m_parsedInputArguments = nullptr;
+          return nullptr;
+        }
+        m_parsedInputArguments->appendVector(
+            StyleValueFactory::cssValueToStyleValueVector(*parsedValue));
+      }
+    }
+  }
+
+  return m_generator->paint(layoutObject, size, zoom, m_parsedInputArguments);
 }
 
 void CSSPaintValue::Observer::paintImageGeneratorReady() {
@@ -73,6 +99,7 @@ DEFINE_TRACE_AFTER_DISPATCH(CSSPaintValue) {
   visitor->trace(m_name);
   visitor->trace(m_generator);
   visitor->trace(m_paintImageGeneratorObserver);
+  visitor->trace(m_parsedInputArguments);
   CSSImageGeneratorValue::traceAfterDispatch(visitor);
 }