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_Object.h b/fpdfsdk/javascript/JS_Object.h
index 1f61918..c6491e2 100644
--- a/fpdfsdk/javascript/JS_Object.h
+++ b/fpdfsdk/javascript/JS_Object.h
@@ -16,7 +16,7 @@
 
 class CJS_Context;
 class CJS_Object;
-class CPDFSDK_Environment;
+class CPDFSDK_FormFillEnvironment;
 
 class CJS_EmbedObj {
  public: