Revert of Use std::unique_ptr.

src/pdf/SkPDFDevice.cpp

Index: src/pdf/SkPDFDevice.cpp
diff --git a/src/pdf/SkPDFDevice.cpp b/src/pdf/SkPDFDevice.cpp
index 86d4d07acbd3f5d9f79ff04d8407c2126ee7f647..e349ce42fb843ad0c5172547a8cd633fbe1abd6a 100644
--- a/src/pdf/SkPDFDevice.cpp
+++ b/src/pdf/SkPDFDevice.cpp
@@ -1533,10 +1533,10 @@
     return mediaBox;
 }
 
-std::unique_ptr<SkStreamAsset> SkPDFDevice::content() const {
+skstd::unique_ptr<SkStreamAsset> SkPDFDevice::content() const {
     SkDynamicMemoryWStream buffer;
     this->writeContent(&buffer);
-    return std::unique_ptr<SkStreamAsset>(
+    return skstd::unique_ptr<SkStreamAsset>(
             buffer.bytesWritten() > 0
             ? buffer.detachAsStream()
             : new SkMemoryStream);