Rename CFX_RetainPtr to RetainPtr

This CL renames CFX_RetainPtr to RetainPtr and places in the fxcrt
namespace.

Bug: pdfium:898
Change-Id: I8798a9f79cb0840d3f037e8d04937cedd742914e
Reviewed-on: https://pdfium-review.googlesource.com/14616
Reviewed-by: Tom Sepez <tsepez@chromium.org>
Commit-Queue: dsinclair <dsinclair@chromium.org>
diff --git a/fpdfsdk/cpdfsdk_formfillenvironment.cpp b/fpdfsdk/cpdfsdk_formfillenvironment.cpp
index 300a742..9e65b46 100644
--- a/fpdfsdk/cpdfsdk_formfillenvironment.cpp
+++ b/fpdfsdk/cpdfsdk_formfillenvironment.cpp
@@ -441,8 +441,8 @@
   return nullptr;
 }
 
-CFX_RetainPtr<IFX_SeekableReadStream>
-CPDFSDK_FormFillEnvironment::DownloadFromURL(const wchar_t* url) {
+RetainPtr<IFX_SeekableReadStream> CPDFSDK_FormFillEnvironment::DownloadFromURL(
+    const wchar_t* url) {
   if (!m_pInfo || !m_pInfo->FFI_DownloadFromURL)
     return nullptr;