Add Cast() for Int32 and Uint32

It should be possible to cast a Value to Int32 without throwing an exception
when IsInt32() is true. Same for Uint32.

BUG=chromium:462402
LOG=Y

Review URL: https://codereview.chromium.org/1003663002

Cr-Commit-Position: refs/heads/master@{#27156}

include/v8.h

@@ -2465,8 +2465,11 @@ class V8_EXPORT Integer : public Number {
 class V8_EXPORT Int32 : public Integer {
  public:
   int32_t Value() const;
+  V8_INLINE static Int32* Cast(v8::Value* obj);
+
  private:
   Int32();
+  static void CheckCast(v8::Value* obj);
 };
 
 
@@ -2476,8 +2479,11 @@ class V8_EXPORT Int32 : public Integer {
 class V8_EXPORT Uint32 : public Integer {
  public:
   uint32_t Value() const;
+  V8_INLINE static Uint32* Cast(v8::Value* obj);
+
  private:
   Uint32();
+  static void CheckCast(v8::Value* obj);
 };
 
 
@@ -7364,6 +7370,22 @@ Integer* Integer::Cast(v8::Value* value) {
 }
 
 
+Int32* Int32::Cast(v8::Value* value) {
+#ifdef V8_ENABLE_CHECKS
+  CheckCast(value);
+#endif
+  return static_cast<Int32*>(value);
+}
+
+
+Uint32* Uint32::Cast(v8::Value* value) {
+#ifdef V8_ENABLE_CHECKS
+  CheckCast(value);
+#endif
+  return static_cast<Uint32*>(value);
+}
+
+
 Date* Date::Cast(v8::Value* value) {
 #ifdef V8_ENABLE_CHECKS
   CheckCast(value);

src/api.cc

@@ -2973,6 +2973,18 @@ void v8::Integer::CheckCast(v8::Value* that) {
 }
 
 
+void v8::Int32::CheckCast(v8::Value* that) {
+  Utils::ApiCheck(that->IsInt32(), "v8::Int32::Cast()",
+                  "Could not convert to 32-bit signed integer");
+}
+
+
+void v8::Uint32::CheckCast(v8::Value* that) {
+  Utils::ApiCheck(that->IsUint32(), "v8::Uint32::Cast()",
+                  "Could not convert to 32-bit unsigned integer");
+}
+
+
 void v8::Array::CheckCast(Value* that) {
   i::Handle<i::Object> obj = Utils::OpenHandle(that);
   Utils::ApiCheck(obj->IsJSArray(),