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

@@ -235,5 +235,19 @@ 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 `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 mExtraAnnotations[CrashReporter::Annotation::OOMAllocationSize]
+             .Length() > 0;
+}
+
 }  // 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