net: Implement canceling of all async operations in FileStream.

tools/valgrind/memcheck/suppressions.txt

 # There are four kinds of suppressions in this file.
 # 1. third party stuff we have no control over
 #
 # 2. intentional unit test errors, or stuff that is somehow a false positive
 # in our own code, or stuff that is so trivial it's not worth fixing
 #
 # 3. Suppressions for real chromium bugs that are not yet fixed.
 # These should all be in chromium's bug tracking system (but a few aren't yet).
 # Periodically we should sweep this file and the bug tracker clean by
 # running overnight and removing outdated bugs/suppressions.
@@ skipping 6005 matching lines @@
    Memcheck:Unaddressable
    ...
    fun:_*Sk*
    ...
    fun:_ZN7WebCore24CanvasRenderingContext2D*
    fun:_ZN7WebCore34CanvasRenderingContext2DV8InternalL11*CallbackERKN2v89ArgumentsE
    fun:_ZN2v88internalL19HandleApiCallHelperILb0EEEPNS0_11MaybeObjectENS0_12_GLOBAL__N_116BuiltinArgumentsILNS0_21BuiltinExtraArgumentsE1EEEPNS0_7IsolateE
    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
    ...
    fun:*SkPath*
    ...
    fun:_ZN8SkDevice8drawRectERK6SkDrawRK6SkRectRK7SkPaint
    fun:_ZN8SkCanvas8drawRectERK6SkRectRK7SkPaint
    fun:_ZN7WebCore15GraphicsContext10strokeRectERKNS_9FloatRectEf
    fun:_ZNK7WebCore13RenderSVGRect11strokeShapeEPNS_15GraphicsContextE
 }
@@ skipping 149 matching lines @@
    Memcheck:Leak
    fun:_Znw*
    ...
    fun:_ZN7fileapi22LocalFileChangeTracker9TrackerDB4InitENS1_14RecoveryOptionE
    fun:_ZN7fileapi22LocalFileChangeTracker9TrackerDB9MarkDirtyERKSs
    fun:_ZN7fileapi22LocalFileChangeTracker19MarkDirtyOnDatabaseERKNS_13FileSystemURLE
    fun:_ZN7fileapi22LocalFileChangeTracker12RecordChangeERKNS_13FileSystemURLERKNS_10FileChangeE
    fun:_ZN7fileapi22LocalFileChangeTracker17OnCreateDirectoryERKNS_13FileSystemURLE
    fun:_ZN7fileapi42LocalFileChangeTrackerTest_GetChanges_Test8TestBodyEv
 }