timer_wrap: Timer.now always update loop time

In `Timer.now` always update the loop time by calling uv_update_time.
Previously we were trying to cache the loop time to prevent extra
syscalls. While a noble goal, it can cause timers to fire early in
certain circumstances. Especially seen in cpu bound work loads or work
loads with synchronous file operations.

src/timer_wrap.cc

@@ -144,6 +144,7 @@ class TimerWrap : public HandleWrap {
 
   static void Now(const FunctionCallbackInfo<Value>& args) {
     HandleScope scope(node_isolate);
+    uv_update_time(uv_default_loop());
     double now = static_cast<double>(uv_now(uv_default_loop()));
     args.GetReturnValue().Set(now);
   }

test/simple/test-timers-first-fire.js

@@ -0,0 +1,33 @@
+// Copyright Joyent, Inc. and other Node contributors.
+//
+// Permission is hereby granted, free of charge, to any person obtaining a
+// copy of this software and associated documentation files (the
+// "Software"), to deal in the Software without restriction, including
+// without limitation the rights to use, copy, modify, merge, publish,
+// distribute, sublicense, and/or sell copies of the Software, and to permit
+// persons to whom the Software is furnished to do so, subject to the
+// following conditions:
+//
+// The above copyright notice and this permission notice shall be included
+// in all copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
+// OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+// MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN
+// NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM,
+// DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR
+// OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE
+// USE OR OTHER DEALINGS IN THE SOFTWARE.
+
+var common = require('../common');
+var assert = require('assert');
+
+var TIMEOUT = 50;
+var last = process.hrtime();
+setTimeout(function() {
+  var hr = process.hrtime(last);
+  var ms = (hr[0] * 1e3) + (hr[1] / 1e6);
+  var delta = ms - TIMEOUT;
+  console.log('timer fired in', delta);
+  assert.ok(delta > 0, 'Timer fired early');
+}, TIMEOUT);