Catch null return value from computeComputedStyle.

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

Index: third_party/WebKit/Source/core/css/CSSComputedStyleDeclaration.cpp
diff --git a/third_party/WebKit/Source/core/css/CSSComputedStyleDeclaration.cpp b/third_party/WebKit/Source/core/css/CSSComputedStyleDeclaration.cpp
index 4d733338f433de011ed701f0c4b22f310c0471a6..0c3dda6c8401ab771c079841d111cfb583c0b6a5 100644
--- a/third_party/WebKit/Source/core/css/CSSComputedStyleDeclaration.cpp
+++ b/third_party/WebKit/Source/core/css/CSSComputedStyleDeclaration.cpp
@@ -531,12 +531,18 @@ Node* CSSComputedStyleDeclaration::styledNode() const
 
 PassRefPtrWillBeRawPtr<CSSValue> CSSComputedStyleDeclaration::getPropertyCSSValue(AtomicString customPropertyName) const
 {
-    return ComputedStyleCSSValueMapping::get(customPropertyName, *computeComputedStyle());
+    const ComputedStyle* style = computeComputedStyle();
+    if (!style)
+        return nullptr;
+    return ComputedStyleCSSValueMapping::get(customPropertyName, *style);
 }
 
 const HashMap<AtomicString, RefPtr<CSSVariableData>>* CSSComputedStyleDeclaration::getVariables() const
 {
-    return ComputedStyleCSSValueMapping::getVariables(*computeComputedStyle());
+    const ComputedStyle* style = computeComputedStyle();
+    if (!style)
+        return nullptr;
+    return ComputedStyleCSSValueMapping::getVariables(*style);
 }
 
 PassRefPtrWillBeRawPtr<CSSValue> CSSComputedStyleDeclaration::getPropertyCSSValue(CSSPropertyID propertyID) const