Bug 1589493 - Expose CrashReporterHost::isLikelyOOM();r=gsvelto

We'll use this method to expose additional information to the front-end for recovering from OOM.

Differential Revision: https://phabricator.services.mozilla.com/D54129

--HG--
extra : moz-landing-system : lando

ipc/glue/CrashReporterHost.cpp

@@ -8,6 +8,7 @@
 #include "CrashReporterMetadataShmem.h"
 #include "mozilla/dom/Promise.h"
 #include "mozilla/recordreplay/ParentIPC.h"
+#include "mozilla/EnumeratedRange.h"
 #include "mozilla/Sprintf.h"
 #include "mozilla/SyncRunnable.h"
 #include "mozilla/Telemetry.h"
@@ -241,5 +242,21 @@ void CrashReporterHost::AddAnnotation(CrashReporter::Annotation aKey,
   mExtraAnnotations[aKey] = aValue;
 }
 
+bool CrashReporterHost::IsLikelyOOM() {
+  // The data is only populated during the call to `FinalizeCrashReport()`.
+  MOZ_ASSERT(mFinalized);
+  if (mExtraAnnotations[CrashReporter::Annotation::OOMAllocationSize].Length() >
+      0) {
+    // If `OOMAllocationSize` was set, we know that the crash happened
+    // because an allocation failed (`malloc` returned `nullptr`).
+    //
+    // As Unix systems generally allow `malloc` to return a non-null value
+    // even when no virtual memory is available, this doesn't cover all
+    // cases of OOM under Unix (far from it).
+    return true;
+  }
+  return false;
+}
+
 }  // namespace ipc
 }  // namespace mozilla

ipc/glue/CrashReporterHost.h

@@ -94,6 +94,14 @@ class CrashReporterHost {
     return mExtraAnnotations[CrashReporter::Annotation::additional_minidumps];
   }
 
+  // Return `true` if this crash reporter has been identified as a likely OOM.
+  //
+  // At the time of this writing, OOMs detection is considered reliable under
+  // Windows but other platforms quite often return false negatives.
+  //
+  // `CrashReporterHost::FinalizeCrashReport()` MUST have been called already.
+  bool IsLikelyOOM();
+
   // This is a static helper function to notify the crash service that a
   // crash has occurred and record the crash with telemetry. This can be called
   // from any thread, and if not called from the main thread, will post a