net: Implement canceling of all async operations in FileStream.

tools/valgrind/memcheck/suppressions.txt

Index: tools/valgrind/memcheck/suppressions.txt
diff --git a/tools/valgrind/memcheck/suppressions.txt b/tools/valgrind/memcheck/suppressions.txt
index 0afda18dad0069c7817b1f9d0f147bf951e0cf51..e1eeca7daf48735092be849e4af3e085f8fe2ad6 100644
--- a/tools/valgrind/memcheck/suppressions.txt
+++ b/tools/valgrind/memcheck/suppressions.txt
@@ -5904,6 +5904,21 @@
    fun:_ZN2v88internalL21Builtin_HandleApiCallENS0_12_GLOBAL__N_116BuiltinArgumentsILNS0_21BuiltinExtraArgumentsE1EEEPNS0_7IsolateE
 }
 {
+   FileStream::Context can leak through WorkerPool by design
+   Memcheck:Leak
+   fun:_Znw*
+   fun:_ZN3net10FileStreamC1EPNS_6NetLogE
+   ...
+}
+{
+   Tasks posted to WorkerPool can leak by design
+   Memcheck:Leak
+   fun:_Znw*
+   fun:_ZN4base8internal20PostTaskAndReplyImpl16PostTaskAndReplyERKN15tracked_objects8LocationERKNS_8CallbackIFvvEEESA_
+   fun:_ZN4base10WorkerPool16PostTaskAndReplyERKN15tracked_objects8LocationERKNS_8CallbackIFvvEEES9_b
+   ...
+}
+{
    bug_149748b
    Memcheck:Unaddressable
    ...