Move commandStartTime from BlazeRuntime to CommandEnvironment.

--
MOS_MIGRATED_REVID=105840775
diff --git a/src/main/java/com/google/devtools/build/lib/buildtool/ExecutionTool.java b/src/main/java/com/google/devtools/build/lib/buildtool/ExecutionTool.java
index cc3c804..bf018f1 100644
--- a/src/main/java/com/google/devtools/build/lib/buildtool/ExecutionTool.java
+++ b/src/main/java/com/google/devtools/build/lib/buildtool/ExecutionTool.java
@@ -440,7 +440,7 @@
       interrupted = true;
       throw e;
     } finally {
-      runtime.recordLastExecutionTime();
+      env.recordLastExecutionTime();
       if (request.isRunningInEmacs()) {
         request.getOutErr().printErrLn("blaze: Leaving directory `" + getExecRoot() + "/'");
       }