Fixing remaining VC++ 2015 64-bit build breaks

chrome/app/chrome_watcher_client_unittest_win.cc

Index: chrome/app/chrome_watcher_client_unittest_win.cc
diff --git a/chrome/app/chrome_watcher_client_unittest_win.cc b/chrome/app/chrome_watcher_client_unittest_win.cc
index e3549e990150687b77da4367bae7777dfc646f72..d9d23c11e0be9f755916b98ac435b23990f611ea 100644
--- a/chrome/app/chrome_watcher_client_unittest_win.cc
+++ b/chrome/app/chrome_watcher_client_unittest_win.cc
@@ -170,12 +170,14 @@ class ChromeWatcherClientThread : public base::SimpleThread {
     base::CommandLine ret = base::GetMultiProcessTestChildBaseCommandLine();
     ret.AppendSwitchASCII(switches::kTestChildProcess,
                           "ChromeWatcherClientTestProcess");
-    ret.AppendSwitchASCII(kEventHandle,
-                          base::UintToString(reinterpret_cast<unsigned int>(
-                              on_initialized_event)));
+    // Cast through uintptr_t and then unsigned int to make the truncation
+    // explicit. Handles are size-of-pointer but are always 32-bit values.
     ret.AppendSwitchASCII(
-        kParentHandle,
-        base::UintToString(reinterpret_cast<unsigned int>(parent_handle)));
+        kEventHandle, base::UintToString(static_cast<unsigned int>(
+                          reinterpret_cast<uintptr_t>(on_initialized_event))));
+    ret.AppendSwitchASCII(kParentHandle,
+                          base::UintToString(static_cast<unsigned int>(
+                              reinterpret_cast<uintptr_t>(parent_handle))));
 
     // Our child does not actually need the main thread ID, but we verify here
     // that the correct ID is being passed from the client.