[inspector] Add byte swapping on BE machines

With https://crrev.com/c/2277142 adding unified
(de)serialization support, "cbor ParseUTF16String" is no longer
being used and byte orders remain in LE format.

This CL essentially reverts some of the changes made here:
https://crrev.com/c/2038716 and re-adds byte swapping
on BE machines.

Change-Id: I3e7be6ba182e7faada3bf31dff9a89c1343abbbc
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2281082
Reviewed-by: Yang Guo <yangguo@chromium.org>
Commit-Queue: Milad Farazmand <miladfar@ca.ibm.com>
Cr-Commit-Position: refs/heads/master@{#68690}

src/inspector/string-16.cc

@@ -208,8 +208,21 @@ String16 String16::fromUTF8(const char* stringStart, size_t length) {
   return String16(UTF8ToUTF16(stringStart, length));
 }
 
-String16 String16::fromUTF16(const UChar* stringStart, size_t length) {
+String16 String16::fromUTF16LE(const UChar* stringStart, size_t length) {
+#ifdef V8_TARGET_BIG_ENDIAN
+  // Need to flip the byte order on big endian machines.
+  String16Builder builder;
+  builder.reserveCapacity(length);
+  for (size_t i = 0; i < length; i++) {
+    const UChar utf16be_char =
+        stringStart[i] << 8 | (stringStart[i] >> 8 & 0x00FF);
+    builder.append(utf16be_char);
+  }
+  return builder.toString();
+#else
+  // No need to do anything on little endian machines.
   return String16(stringStart, length);
+#endif  // V8_TARGET_BIG_ENDIAN
 }
 
 std::string String16::utf8() const {

src/inspector/string-16.h

@@ -70,7 +70,11 @@ class String16 {
   // Convenience methods.
   V8_EXPORT std::string utf8() const;
   V8_EXPORT static String16 fromUTF8(const char* stringStart, size_t length);
-  V8_EXPORT static String16 fromUTF16(const UChar* stringStart, size_t length);
+
+  // Instantiates a String16 in native endianness from UTF16 LE.
+  // On Big endian architectures, byte order needs to be flipped.
+  V8_EXPORT static String16 fromUTF16LE(const UChar* stringStart,
+                                        size_t length);
 
   std::size_t hash() const {
     if (!hash_code) {

src/inspector/string-util.h

@@ -30,7 +30,7 @@ class StringUtil {
   }
 
   static String fromUTF16LE(const uint16_t* data, size_t length) {
-    return String16::fromUTF16(data, length);
+    return String16::fromUTF16LE(data, length);
   }
 
   static const uint8_t* CharactersLatin1(const String& s) { return nullptr; }