Add some missing const in CFXJSE_Context

These were declared non-const since there is likely a missing const
in the v8 API that these are used in. Reduces a small amount of
global writable data.

-- rename to k-style names while at it.

Change-Id: I800cea0a8f23fd319bf4c5f70b78465e151f7e9d
Reviewed-on: https://pdfium-review.googlesource.com/c/pdfium/+/74831
Reviewed-by: Lei Zhang <thestig@chromium.org>
Commit-Queue: Tom Sepez <tsepez@chromium.org>

fxjs/README

diff --git a/fxjs/README b/fxjs/README
index a1cfe32..fb49f59 100644
--- a/fxjs/README
+++ b/fxjs/README
@@ -20,8 +20,8 @@
 objects, regardless of the FXJS/FXJSE distinction.  Slot 0 is the
 tag and contains either:
   kPerObjectDataTag for FXJS objects, or
-  g_FXJSEHostObjectTag for FXJSE Host objects, or
-  g_FXJSEProxyObjectTag for a global proxy object under FXJSE, or
+  kFXJSEHostObjectTag for FXJSE Host objects, or
+  kFXJSEProxyObjectTag for a global proxy object under FXJSE, or
   One of 4 specific FXJSE_CLASS_DESCRIPTOR globals for FXJSE classes:
     GlobalClassDescriptor
     NormalClassDescriptor
@@ -30,10 +30,10 @@
 
 Slot 1's contents are determined by these tags:
   kPerObjectDataTag means an aligned pointer to CFXJS_PerObjectData.
-  g_FXJSEHostObjectTag means an aligned pointer to CFXJSE_HostObject.
-  g_FXJSEProxyObjectTag means nullptr, and to check the prototype instead.
+  kFXJSEHostObjectTag means an aligned pointer to CFXJSE_HostObject.
+  kFXJSEProxyObjectTag means nullptr, and to check the prototype instead.
   A FXJSE_CLASS_DESCRIPTOR pointer means to expect an actual v8 function
-  object (or a string naming that function),  and not an aligned pointer.
+  object (or a string naming that function), and not an aligned pointer.
 
 Because PDFium uses V8 for various unrelated purposes, there may be up to
 four v8::Contexts (JS Global Objects) associated with each document. One is

fxjs/xfa/cfxjse_context.cpp

diff --git a/fxjs/xfa/cfxjse_context.cpp b/fxjs/xfa/cfxjse_context.cpp
index 26a07e9..3ea9a18 100644
--- a/fxjs/xfa/cfxjse_context.cpp
+++ b/fxjs/xfa/cfxjse_context.cpp
@@ -55,8 +55,8 @@
     "};";
 
 // Only address matters, values are for humans debuging here.
-char g_FXJSEHostObjectTag[] = "FXJSE Host Object";
-char g_FXJSEProxyObjectTag[] = "FXJSE Proxy Object";
+const char kFXJSEHostObjectTag[] = "FXJSE Host Object";
+const char kFXJSEProxyObjectTag[] = "FXJSE Proxy Object";
 
 v8::Local<v8::Object> CreateReturnValue(v8::Isolate* pIsolate,
                                         v8::TryCatch* trycatch) {
@@ -127,7 +127,8 @@
 void FXJSE_UpdateProxyBinding(v8::Local<v8::Object> hObject) {
   ASSERT(!hObject.IsEmpty());
   ASSERT(hObject->InternalFieldCount() == 2);
-  hObject->SetAlignedPointerInInternalField(0, g_FXJSEProxyObjectTag);
+  hObject->SetAlignedPointerInInternalField(
+      0, const_cast<char*>(kFXJSEProxyObjectTag));
   hObject->SetAlignedPointerInInternalField(1, nullptr);
 }
 
@@ -137,7 +138,8 @@
                                CFXJSE_HostObject* lpNewBinding) {
   ASSERT(!hObject.IsEmpty());
   ASSERT(hObject->InternalFieldCount() == 2);
-  hObject->SetAlignedPointerInInternalField(0, g_FXJSEHostObjectTag);
+  hObject->SetAlignedPointerInInternalField(
+      0, const_cast<char*>(kFXJSEHostObjectTag));
   hObject->SetAlignedPointerInInternalField(1, lpNewBinding);
 }
 
@@ -156,7 +158,7 @@
 
   v8::Local<v8::Object> hObject = hJSObject;
   if (hObject->InternalFieldCount() != 2 ||
-      hObject->GetAlignedPointerFromInternalField(0) == g_FXJSEProxyObjectTag) {
+      hObject->GetAlignedPointerFromInternalField(0) == kFXJSEProxyObjectTag) {
     v8::Local<v8::Value> hProtoObject = hObject->GetPrototype();
     if (hProtoObject.IsEmpty() || !hProtoObject->IsObject())
       return nullptr;
@@ -165,7 +167,7 @@
     if (hObject->InternalFieldCount() != 2)
       return nullptr;
   }
-  if (hObject->GetAlignedPointerFromInternalField(0) != g_FXJSEHostObjectTag)
+  if (hObject->GetAlignedPointerFromInternalField(0) != kFXJSEHostObjectTag)
     return nullptr;
 
   return static_cast<CFXJSE_HostObject*>(