Add a new priority level, THROTTLED, below IDLE.

net/base/request_priority.h

Index: net/base/request_priority.h
diff --git a/net/base/request_priority.h b/net/base/request_priority.h
index dcf7793642336f1540a6e3eff2ea7035b8b569da..3ce1f22f3ad9015919ccf2238eb5db71eb8fceca 100644
--- a/net/base/request_priority.h
+++ b/net/base/request_priority.h
@@ -16,8 +16,12 @@ namespace net {
 // GENERATED_JAVA_CLASS_NAME_OVERRIDE: RequestPriority
 // GENERATED_JAVA_PREFIX_TO_STRIP:
 enum RequestPriority {
-  IDLE = 0,
-  MINIMUM_PRIORITY = IDLE,
+  THROTTLED = 0,  // Used to signal that resources
+                  // should be reserved for following
+                  // requests (i.e. that higher priority
+                  // following requests are expected).
+  MINIMUM_PRIORITY = THROTTLED,
+  IDLE,  // Default "as resources available" level.
   LOWEST,
   DEFAULT_PRIORITY = LOWEST,
   LOW,