Implement timeouts on Windows.

Makes #1664 much less acute.

--
MOS_MIGRATED_REVID=130750731
diff --git a/src/main/java/com/google/devtools/build/lib/shell/Subprocess.java b/src/main/java/com/google/devtools/build/lib/shell/Subprocess.java
index e5710e7..769b6b5 100644
--- a/src/main/java/com/google/devtools/build/lib/shell/Subprocess.java
+++ b/src/main/java/com/google/devtools/build/lib/shell/Subprocess.java
@@ -53,6 +53,11 @@
   boolean finished();
 
   /**
+   * Returns if the process timed out.
+   */
+  boolean timedout();
+
+  /**
    * Waits for the process to finish.
    */
   void waitFor() throws InterruptedException;