Bug 1428612 - Part 2: Add an assertion to check the histogram name pointer. r=gfritzsche

This adds a dignostic assertion that the name pointer is actually within the
static name table.

--HG--
extra : rebase_source : 4f82f72c83444a3ccd5be270080837f60110766e

toolkit/components/telemetry/TelemetryHistogram.cpp

@@ -1741,6 +1741,11 @@ void TelemetryHistogram::InitializeGlobalState(bool canRecordBase,
   for (uint32_t i = 0; i < HistogramCount; i++) {
     auto name = gHistogramInfos[i].name();
 
+    // Make sure the name pointer is in a valid region. See bug 1428612.
+    MOZ_DIAGNOSTIC_ASSERT(name >= gHistogramStringTable);
+    MOZ_DIAGNOSTIC_ASSERT(
+        uintptr_t(name) < (uintptr_t(gHistogramStringTable) + sizeof(gHistogramStringTable)));
+
     nsCString wrappedName;
     wrappedName.AssignLiteral(name, strlen(name));
     gNameToHistogramIDMap.Put(wrappedName, HistogramID(i));