Avoid crash during PaintController::showDebugData()

third_party/WebKit/Source/platform/graphics/paint/PaintController.cpp

Index: third_party/WebKit/Source/platform/graphics/paint/PaintController.cpp
diff --git a/third_party/WebKit/Source/platform/graphics/paint/PaintController.cpp b/third_party/WebKit/Source/platform/graphics/paint/PaintController.cpp
index 6451c65bccb4e53add10c2257a436430dbb35b2b..bfdf1493246dcdf0406668549653524eef1f31b6 100644
--- a/third_party/WebKit/Source/platform/graphics/paint/PaintController.cpp
+++ b/third_party/WebKit/Source/platform/graphics/paint/PaintController.cpp
@@ -563,8 +563,10 @@ WTF::String PaintController::displayItemListAsDebugString(const DisplayItemList&
             stringBuilder.append(",\n");
         stringBuilder.append(String::format("{index: %d, ", (int)i));
         displayItem.dumpPropertiesAsDebugString(stringBuilder);
-        stringBuilder.append(", cacheIsValid: ");
-        stringBuilder.append(clientCacheIsValid(displayItem.client()) ? "true" : "false");
+        if (displayItem.hasValidClient()) {
+            stringBuilder.append(", cacheIsValid: ");
+            stringBuilder.append(clientCacheIsValid(displayItem.client()) ? "true" : "false");
+        }
         stringBuilder.append('}');
     }
     return stringBuilder.toString();