[sample] fix potential memory leak.

R=petermarshall@chromium.org

Bug: v8:7433
Change-Id: Ibeef2c6855b8ffb6076be889a859da513877171f
Reviewed-on: https://chromium-review.googlesource.com/928563
Commit-Queue: Yang Guo <yangguo@chromium.org>
Reviewed-by: Peter Marshall <petermarshall@chromium.org>
Cr-Commit-Position: refs/heads/master@{#51429}

samples/process.cc

@@ -650,10 +650,10 @@ MaybeLocal<String> ReadFile(Isolate* isolate, const string& name) {
   size_t size = ftell(file);
   rewind(file);
 
-  char* chars = new char[size + 1];
-  chars[size] = '\0';
+  std::unique_ptr<char> chars(new char[size + 1]);
+  chars.get()[size] = '\0';
   for (size_t i = 0; i < size;) {
-    i += fread(&chars[i], 1, size - i, file);
+    i += fread(&chars.get()[i], 1, size - i, file);
     if (ferror(file)) {
       fclose(file);
       return MaybeLocal<String>();
@@ -661,8 +661,7 @@ MaybeLocal<String> ReadFile(Isolate* isolate, const string& name) {
   }
   fclose(file);
   MaybeLocal<String> result = String::NewFromUtf8(
-      isolate, chars, NewStringType::kNormal, static_cast<int>(size));
-  delete[] chars;
+      isolate, chars.get(), NewStringType::kNormal, static_cast<int>(size));
   return result;
 }