Add new BuildMetrics event to BEP.

To start we add just a single metric, the number of actions constructed in the current build.

RELNOTES: None
PiperOrigin-RevId: 201248490
diff --git a/src/main/java/com/google/devtools/build/lib/analysis/BuildView.java b/src/main/java/com/google/devtools/build/lib/analysis/BuildView.java
index c223113..204d949 100644
--- a/src/main/java/com/google/devtools/build/lib/analysis/BuildView.java
+++ b/src/main/java/com/google/devtools/build/lib/analysis/BuildView.java
@@ -160,6 +160,10 @@
     return skyframeBuildView.getEvaluatedTargetKeys().size();
   }
 
+  public int getActionsConstructed() {
+    return skyframeBuildView.getEvaluatedActionCount();
+  }
+
   public PackageManagerStatistics getAndClearPkgManagerStatistics() {
     return skyframeExecutor.getPackageManager().getAndClearStatistics();
   }
@@ -196,6 +200,7 @@
     pollInterruptedStatus();
 
     skyframeBuildView.resetEvaluatedConfiguredTargetKeysSet();
+    skyframeBuildView.resetEvaluationActionCount();
 
     Collection<Target> targets = loadingResult.getTargets();
     eventBus.post(new AnalysisPhaseStartedEvent(targets));