Prevent unitialized variable.

R=hablich@chromium.org

Bug: chromium:646005
Change-Id: I425111cb393d0119fa18fbe14bc32d5e7560b181
Reviewed-on: https://chromium-review.googlesource.com/667157
Commit-Queue: Michael Hablich <hablich@chromium.org>
Reviewed-by: Michael Hablich <hablich@chromium.org>
Cr-Commit-Position: refs/heads/master@{#48206}

src/base/platform/time.cc

@@ -621,6 +621,8 @@ TimeTicks TimeTicks::HighResolutionNow() {
   ticks = (gethrtime() / Time::kNanosecondsPerMicrosecond);
 #elif V8_OS_POSIX
   ticks = ClockNow(CLOCK_MONOTONIC);
+#else
+#error platform does not implement TimeTicks::HighResolutionNow.
 #endif  // V8_OS_MACOSX
   // Make sure we never return 0 here.
   return TimeTicks(ticks + 1);