Rename CPDFSDK_Environment to CPDFSDK_FormfillEnvironment

Rename CPDFSDK_Environment to make it explicit that this is part of the formfill
system.

Review-Url: https://codereview.chromium.org/2391313002
diff --git a/fpdfsdk/javascript/JS_Runtime_Stub.cpp b/fpdfsdk/javascript/JS_Runtime_Stub.cpp
index 8d8ac33..ec52a8b 100644
--- a/fpdfsdk/javascript/JS_Runtime_Stub.cpp
+++ b/fpdfsdk/javascript/JS_Runtime_Stub.cpp
@@ -164,6 +164,6 @@
 void IJS_Runtime::Destroy() {}
 
 // static
-IJS_Runtime* IJS_Runtime::Create(CPDFSDK_Environment* pEnv) {
+IJS_Runtime* IJS_Runtime::Create(CPDFSDK_FormFillEnvironment* pEnv) {
   return new CJS_RuntimeStub;
 }