Make CPDF_Dictionary methods take CFX_ByteString arguments

This will help avoid duplicate allocation of CFX_ByteStrings
when the caller already has one.  It may seem counter-intuitive
that requiring the caller to pass an allocated CFX_ByteString
rather than a static CFX_ByteStringC would improve the situation,
but due to the idiosyncrasies of std::map, the CPDF_Dictionary
methods must always do an allocation under the covers which
can't be avoided.

The changed callers in this CL are places where we would
previously demote to CFX_ByteStringC and then allocate a
a duplicate CFX_ByteString in the dictionary method.

Review URL: https://codereview.chromium.org/1889863002
diff --git a/fpdfsdk/fsdk_baseform.cpp b/fpdfsdk/fsdk_baseform.cpp
index 288a2fe..7487cdd 100644
--- a/fpdfsdk/fsdk_baseform.cpp
+++ b/fpdfsdk/fsdk_baseform.cpp
@@ -461,7 +461,7 @@
     case FIELDTYPE_CHECKBOX:
     case FIELDTYPE_RADIOBUTTON:
       if (CPDF_Dictionary* pSubDict = psub->AsDictionary()) {
-        return !!pSubDict->GetStreamBy(GetAppState().AsStringC());
+        return !!pSubDict->GetStreamBy(GetAppState());
       }
       return FALSE;
   }
@@ -1808,7 +1808,7 @@
   ASSERT(pDoc);
 
   CPDF_Dictionary* pAPDict = m_pAnnot->GetAnnotDict()->GetDictBy("AP");
-  CPDF_Stream* pStream = pAPDict->GetStreamBy(sAPType.AsStringC());
+  CPDF_Stream* pStream = pAPDict->GetStreamBy(sAPType);
   CPDF_Dictionary* pStreamDict = pStream->GetDict();
   CFX_ByteString sImageAlias = "IMG";
 
@@ -1826,15 +1826,14 @@
 
   if (pStreamResList) {
     CPDF_Dictionary* pXObject = new CPDF_Dictionary;
-    pXObject->SetAtReference(sImageAlias.AsStringC(), pDoc, pImage);
+    pXObject->SetAtReference(sImageAlias, pDoc, pImage);
     pStreamResList->SetAt("XObject", pXObject);
   }
 }
 
 void CPDFSDK_Widget::RemoveAppearance(const CFX_ByteString& sAPType) {
-  if (CPDF_Dictionary* pAPDict = m_pAnnot->GetAnnotDict()->GetDictBy("AP")) {
-    pAPDict->RemoveAt(sAPType.AsStringC());
-  }
+  if (CPDF_Dictionary* pAPDict = m_pAnnot->GetAnnotDict()->GetDictBy("AP"))
+    pAPDict->RemoveAt(sAPType);
 }
 
 FX_BOOL CPDFSDK_Widget::OnAAction(CPDF_AAction::AActionType type,