Merge to XFA: Add type cast definitions for CPDF_Stream.

This Cl adds ToStream, CPDF_Object::AsStream and CPDF_Object::IsStream and
updates the src to use them as needed.

BUG=pdfium:201
R=tsepez@chromium.org

Review URL: https://codereview.chromium.org/1402413004 .

(cherry picked from commit 338805f1366dcdf9a5b48cf591541cf98d7490f1)

Review URL: https://codereview.chromium.org/1422513004 .

3 files changed, 23 insertions, 29 deletions

diff --git a/core/src/fpdfdoc/doc_annot.cpp b/core/src/fpdfdoc/doc_annot.cpp
index ca05d783b8..dc5ccb811c 100644
--- a/core/src/fpdfdoc/doc_annot.cpp
+++ b/core/src/fpdfdoc/doc_annot.cpp
@@ -190,22 +190,20 @@ CPDF_Stream* FPDFDOC_GetAnnotAP(CPDF_Dictionary* pAnnotDict,
     return NULL;
   }
   const FX_CHAR* ap_entry = "N";
-  if (mode == CPDF_Annot::Down) {
+  if (mode == CPDF_Annot::Down)
     ap_entry = "D";
-  } else if (mode == CPDF_Annot::Rollover) {
+  else if (mode == CPDF_Annot::Rollover)
     ap_entry = "R";
-  }
-  if (!pAP->KeyExist(ap_entry)) {
+  if (!pAP->KeyExist(ap_entry))
     ap_entry = "N";
-  }
+
   CPDF_Object* psub = pAP->GetElementValue(ap_entry);
-  if (psub == NULL) {
-    return NULL;
-  }
-  CPDF_Stream* pStream = NULL;
-  if (psub->GetType() == PDFOBJ_STREAM) {
-    pStream = (CPDF_Stream*)psub;
-  } else if (CPDF_Dictionary* pDict = psub->AsDictionary()) {
+  if (!psub)
+    return nullptr;
+  if (CPDF_Stream* pStream = psub->AsStream())
+    return pStream;
+
+  if (CPDF_Dictionary* pDict = psub->AsDictionary()) {
     CFX_ByteString as = pAnnotDict->GetString("AS");
     if (as.IsEmpty()) {
       CFX_ByteString value = pAnnotDict->GetString(FX_BSTRC("V"));
@@ -213,15 +211,14 @@ CPDF_Stream* FPDFDOC_GetAnnotAP(CPDF_Dictionary* pAnnotDict,
         CPDF_Dictionary* pDict = pAnnotDict->GetDict(FX_BSTRC("Parent"));
         value = pDict ? pDict->GetString(FX_BSTRC("V")) : CFX_ByteString();
       }
-      if (value.IsEmpty() || !pDict->KeyExist(value)) {
+      if (value.IsEmpty() || !pDict->KeyExist(value))
         as = FX_BSTRC("Off");
-      } else {
+      else
         as = value;
-      }
     }
-    pStream = pDict->GetStream(as);
+    return pDict->GetStream(as);
   }
-  return pStream;
+  return nullptr;
 }
 CPDF_Form* CPDF_Annot::GetAPForm(const CPDF_Page* pPage, AppearanceMode mode) {
   CPDF_Stream* pStream = FPDFDOC_GetAnnotAP(m_pAnnotDict, mode);
diff --git a/core/src/fpdfdoc/doc_basic.cpp b/core/src/fpdfdoc/doc_basic.cpp
index b32e34bb4c..414f5749d0 100644
--- a/core/src/fpdfdoc/doc_basic.cpp
+++ b/core/src/fpdfdoc/doc_basic.cpp
@@ -380,15 +380,13 @@ CFX_WideString FILESPEC_EncodeFileName(const CFX_WideStringC& filepath) {
 #endif
 }
 CPDF_Stream* CPDF_FileSpec::GetFileStream() const {
-  if (m_pObj == NULL) {
-    return NULL;
-  }
-  int32_t iType = m_pObj->GetType();
-  if (iType == PDFOBJ_STREAM)
-    return (CPDF_Stream*)m_pObj;
+  if (!m_pObj)
+    return nullptr;
+  if (CPDF_Stream* pStream = m_pObj->AsStream())
+    return pStream;
   if (CPDF_Dictionary* pEF = m_pObj->AsDictionary()->GetDict(FX_BSTRC("EF")))
     return pEF->GetStream(FX_BSTRC("F"));
-  return NULL;
+  return nullptr;
 }
 static void FPDFDOC_FILESPEC_SetFileName(CPDF_Object* pObj,
                                          const CFX_WideStringC& wsFileName,
diff --git a/core/src/fpdfdoc/doc_tagged.cpp b/core/src/fpdfdoc/doc_tagged.cpp
index 2b20e07bb8..f74aa7f6f5 100644
--- a/core/src/fpdfdoc/doc_tagged.cpp
+++ b/core/src/fpdfdoc/doc_tagged.cpp
@@ -317,8 +317,8 @@ static CPDF_Dictionary* FindAttrDict(CPDF_Object* pAttrs,
   CPDF_Dictionary* pDict = nullptr;
   if (pAttrs->IsDictionary()) {
     pDict = pAttrs->AsDictionary();
-  } else if (pAttrs->GetType() == PDFOBJ_STREAM) {
-    pDict = ((CPDF_Stream*)pAttrs)->GetDict();
+  } else if (CPDF_Stream* pStream = pAttrs->AsStream()) {
+    pDict = pStream->GetDict();
   } else if (CPDF_Array* pArray = pAttrs->AsArray()) {
     for (FX_DWORD i = 0; i < pArray->GetCount(); i++) {
       CPDF_Object* pElement = pArray->GetElementValue(i);
@@ -327,10 +327,9 @@ static CPDF_Dictionary* FindAttrDict(CPDF_Object* pAttrs,
         return pDict;
     }
   }
-  if (pDict && pDict->GetString(FX_BSTRC("O")) == owner) {
+  if (pDict && pDict->GetString(FX_BSTRC("O")) == owner)
     return pDict;
-  }
-  return NULL;
+  return nullptr;
 }
 CPDF_Object* CPDF_StructElementImpl::GetAttr(const CFX_ByteStringC& owner,
                                              const CFX_ByteStringC& name,