Bug 1171722 - Part 1: Add gcreason to GCSliceCallback. r=fitzgen

js/public/GCAPI.h

@@ -332,9 +332,10 @@ enum GCProgress {
 struct JS_PUBLIC_API(GCDescription) {
     bool isCompartment_;
     JSGCInvocationKind invocationKind_;
+    gcreason::Reason reason_;
 
-    GCDescription(bool isCompartment, JSGCInvocationKind kind)
-      : isCompartment_(isCompartment), invocationKind_(kind) {}
+    GCDescription(bool isCompartment, JSGCInvocationKind kind, gcreason::Reason reason)
+      : isCompartment_(isCompartment), invocationKind_(kind), reason_(reason) {}
 
     char16_t* formatSliceMessage(JSRuntime* rt) const;
     char16_t* formatSummaryMessage(JSRuntime* rt) const;

js/src/gc/Statistics.cpp

@@ -945,7 +945,7 @@ Statistics::beginSlice(const ZoneGCStats& zoneStats, JSGCInvocationKind gckind,
         bool wasFullGC = zoneStats.isCollectingAllZones();
         if (sliceCallback)
             (*sliceCallback)(runtime, first ? JS::GC_CYCLE_BEGIN : JS::GC_SLICE_BEGIN,
-                             JS::GCDescription(!wasFullGC, gckind));
+                             JS::GCDescription(!wasFullGC, gckind, reason));
     }
 }
 
@@ -977,7 +977,7 @@ Statistics::endSlice()
         bool wasFullGC = zoneStats.isCollectingAllZones();
         if (sliceCallback)
             (*sliceCallback)(runtime, last ? JS::GC_CYCLE_END : JS::GC_SLICE_END,
-                             JS::GCDescription(!wasFullGC, gckind));
+                             JS::GCDescription(!wasFullGC, gckind, slices.back().reason));
     }
 
     /* Do this after the slice callback since it uses these values. */