Bug 945152 - Part 2: Report mapped array buffer statistics for about:memory. r=njn

js/public/MemoryMetrics.h

@@ -123,6 +123,7 @@ struct ObjectsExtraSizes
     macro(Objects, NotLiveGCThing, mallocHeapElementsNonAsmJS) \
     macro(Objects, NotLiveGCThing, mallocHeapElementsAsmJS) \
     macro(Objects, NotLiveGCThing, nonHeapElementsAsmJS) \
+    macro(Objects, NotLiveGCThing, nonHeapElementsMapped) \
     macro(Objects, NotLiveGCThing, nonHeapCodeAsmJS) \
     macro(Objects, NotLiveGCThing, mallocHeapAsmJSModuleData) \
     macro(Objects, NotLiveGCThing, mallocHeapArgumentsData) \

js/src/jsobj.cpp

@@ -5908,6 +5908,8 @@ JSObject::addSizeOfExcludingThis(mozilla::MallocSizeOf mallocSizeOf, JS::Objects
 #else
             sizes->mallocHeapElementsAsmJS += mallocSizeOf(elements);
 #endif
+        } else if (MOZ_UNLIKELY(elements->isMappedArrayBuffer())) {
+            sizes->nonHeapElementsMapped += as<ArrayBufferObject>().byteLength();
         } else {
             sizes->mallocHeapElementsNonAsmJS += mallocSizeOf(elements);
         }

js/xpconnect/src/XPCJSRuntime.cpp

@@ -2139,6 +2139,12 @@ ReportCompartmentStats(const JS::CompartmentStats &cStats,
             "the GC heap.");
     }
 
+    if (cStats.objectsExtra.nonHeapElementsMapped > 0) {
+        REPORT_BYTES(cJSPathPrefix + NS_LITERAL_CSTRING("objects/non-heap/elements/mapped"),
+            KIND_NONHEAP, cStats.objectsExtra.nonHeapElementsMapped,
+            "Memory-mapped array buffer elements.");
+    }
+
     REPORT_BYTES(cJSPathPrefix + NS_LITERAL_CSTRING("objects/non-heap/code/asm.js"),
         KIND_NONHEAP, cStats.objectsExtra.nonHeapCodeAsmJS,
         "AOT-compiled asm.js code.");