check for big sizes in NewData

src/core/SkData.cpp

Index: src/core/SkData.cpp
diff --git a/src/core/SkData.cpp b/src/core/SkData.cpp
index dfbd00384975d93a622c7eabeccfaf5d8b091bd0..ad79ce05350064b128a4e210f7b4ef135ee896af 100644
--- a/src/core/SkData.cpp
+++ b/src/core/SkData.cpp
@@ -63,7 +63,14 @@ SkData* SkData::PrivateNewWithCopy(const void* srcOrNull, size_t length) {
     if (0 == length) {
         return SkData::NewEmpty();
     }
-    char* storage = (char*)sk_malloc_throw(sizeof(SkData) + length);
+
+    const size_t actualLength = length + sizeof(SkData);
+    if (actualLength < length) {
+        // we overflowed
+        sk_throw();
+    }
+
+    char* storage = (char*)sk_malloc_throw(actualLength);
     SkData* data = new (storage) SkData(length);
     if (srcOrNull) {
         memcpy(data->writable_data(), srcOrNull, length);