Bug 1536154 - Make nsStringInputStream always report the full memory size of the backing string r=baku

Give nsIStringStream separate SizeOfIncludingThisIfUnshared and SizeOfIncludingThisEvenIfShared methods. Use the former for memory reporting and the latter for JS engine memory accounting.

Differential Revision: https://phabricator.services.mozilla.com/D29336

dom/file/StreamBlobImpl.cpp

@@ -146,7 +146,7 @@ StreamBlobImpl::CollectReports(nsIHandleReportCallback* aHandleReport,
 
   MOZ_COLLECT_REPORT(
       "explicit/dom/memory-file-data/stream", KIND_HEAP, UNITS_BYTES,
-      stringInputStream->SizeOfIncludingThis(MallocSizeOf),
+      stringInputStream->SizeOfIncludingThisIfUnshared(MallocSizeOf),
       "Memory used to back a File/Blob based on an input stream.");
 
   return NS_OK;
@@ -159,7 +159,7 @@ size_t StreamBlobImpl::GetAllocationSize() const {
     return 0;
   }
 
-  return stringInputStream->SizeOfIncludingThis(MallocSizeOf);
+  return stringInputStream->SizeOfIncludingThisEvenIfShared(MallocSizeOf);
 }
 
 void StreamBlobImpl::GetBlobImplType(nsAString& aBlobImplType) const {

xpcom/io/nsIStringStream.idl

@@ -62,5 +62,8 @@ interface nsIStringInputStream : nsIInputStream
     [noscript] void shareData(in string data, in long dataLen);
 
     [noscript, notxpcom]
-    size_t SizeOfIncludingThis(in MallocSizeOf aMallocSizeOf);
+    size_t SizeOfIncludingThisIfUnshared(in MallocSizeOf aMallocSizeOf);
+
+    [noscript, notxpcom]
+    size_t SizeOfIncludingThisEvenIfShared(in MallocSizeOf aMallocSizeOf);
 };

xpcom/io/nsStringStream.cpp

@@ -196,7 +196,7 @@ nsStringInputStream::ShareData(const char* aData, int32_t aDataLen) {
 }
 
 NS_IMETHODIMP_(size_t)
-nsStringInputStream::SizeOfIncludingThis(MallocSizeOf aMallocSizeOf) {
+nsStringInputStream::SizeOfIncludingThisIfUnshared(MallocSizeOf aMallocSizeOf) {
   ReentrantMonitorAutoEnter lock(mMon);
 
   size_t n = aMallocSizeOf(this);
@@ -204,6 +204,16 @@ nsStringInputStream::SizeOfIncludingThis(MallocSizeOf aMallocSizeOf) {
   return n;
 }
 
+NS_IMETHODIMP_(size_t)
+nsStringInputStream::SizeOfIncludingThisEvenIfShared(
+    MallocSizeOf aMallocSizeOf) {
+  ReentrantMonitorAutoEnter lock(mMon);
+
+  size_t n = aMallocSizeOf(this);
+  n += mData.SizeOfExcludingThisEvenIfShared(aMallocSizeOf);
+  return n;
+}
+
 /////////
 // nsIInputStream implementation
 /////////