Fix uint32_t overflow in task manager UI.

A uint32_t was being multiplied by 1024, and then implicitly cast to uint64_t.
Instead, first explicitly cast to uint64_t, then multiply by 1024.

Bug: 798234
Change-Id: I93188aca5b1169eeed2e91ef68f9d1a007a6e48b
Reviewed-on: https://chromium-review.googlesource.com/848233Reviewed-by: Ahmed Fakhry <afakhry@chromium.org>
Commit-Queue: Erik Chen <erikchen@chromium.org>
Cr-Commit-Position: refs/heads/master@{#526597}

chrome/browser/task_manager/sampling/task_manager_impl.cc

@@ -524,7 +524,8 @@ void TaskManagerImpl::OnReceivedMemoryDump(
     auto it = task_groups_by_proc_id_.find(pmd->pid);
     if (it == task_groups_by_proc_id_.end())
       continue;
-    it->second->set_footprint_bytes(pmd->os_dump->private_footprint_kb * 1024);
+    it->second->set_footprint_bytes(
+        static_cast<uint64_t>(pmd->os_dump->private_footprint_kb) * 1024);
   }
 }