Bug 1552900 - Crash on OOM in ICU on Nightly builds; r=jandem,platform-i18n-reviewers

We're seeing inconsistent handling of OOMs in the ICU library. This
patch changes the behaviour to crash on OOM rather than allowing
ICU to handle the allocation failure. The inconsistent handling in ICU
could lead to ICU being in an inconsistent state which could in turn
cause security problems. The safer alternative is to crash, but it's
possible this will lead to too high of crash rate. For now, we'll try
this on Nightly only and monitor crash reports to see what impact this
change has.

Differential Revision: https://phabricator.services.mozilla.com/D186226

xpcom/build/XPCOMInit.cpp

@@ -163,11 +163,27 @@ class ICUReporter final : public nsIMemoryReporter,
   NS_DECL_ISUPPORTS
 
   static void* Alloc(const void*, size_t aSize) {
+#ifdef NIGHTLY_BUILD
+    void* result = CountingMalloc(aSize);
+    if (result == nullptr) {
+      MOZ_CRASH("Ran out of memory while allocating for ICU");
+    }
+    return result;
+#else
     return CountingMalloc(aSize);
+#endif
   }
 
   static void* Realloc(const void*, void* aPtr, size_t aSize) {
+#ifdef NIGHTLY_BUILD
+    void* result = CountingRealloc(aPtr, aSize);
+    if (result == nullptr) {
+      MOZ_CRASH("Ran out of memory while reallocating for ICU");
+    }
+    return result;
+#else
     return CountingRealloc(aPtr, aSize);
+#endif
   }
 
   static void Free(const void*, void* aPtr) { return CountingFree(aPtr); }