v8: fix --max_old_space_size=4096 integer overflow

See https://code.google.com/p/v8/issues/detail?id=3857 for the bug
report and https://codereview.chromium.org/897543002 for the CL.

PR-URL: #1166
Reviewed-By: Fedor Indutny <fedor@indutny.com>

deps/v8/src/heap/heap.cc

@@ -5082,21 +5082,22 @@ bool Heap::ConfigureHeap(int max_semi_space_size, int max_old_space_size,
     max_semi_space_size_ = max_semi_space_size * MB;
   }
   if (max_old_space_size > 0) {
-    max_old_generation_size_ = max_old_space_size * MB;
+    max_old_generation_size_ = static_cast<intptr_t>(max_old_space_size) * MB;
   }
   if (max_executable_size > 0) {
-    max_executable_size_ = max_executable_size * MB;
+    max_executable_size_ = static_cast<intptr_t>(max_executable_size) * MB;
   }
 
   // If max space size flags are specified overwrite the configuration.
   if (FLAG_max_semi_space_size > 0) {
     max_semi_space_size_ = FLAG_max_semi_space_size * MB;
   }
   if (FLAG_max_old_space_size > 0) {
-    max_old_generation_size_ = FLAG_max_old_space_size * MB;
+    max_old_generation_size_ =
+        static_cast<intptr_t>(FLAG_max_old_space_size) * MB;
   }
   if (FLAG_max_executable_size > 0) {
-    max_executable_size_ = FLAG_max_executable_size * MB;
+    max_executable_size_ = static_cast<intptr_t>(FLAG_max_executable_size) * MB;
   }
 
   if (FLAG_stress_compaction) {