common-mk: Add power_manager to platform.gyp.

BUG=chromium:328740
TEST=did a build
CQ-DEPEND=I84437b0b949f4053f5bdf70aa938274fd3cc58a0
CQ-DEPEND=I221469094a24015b8cc5a6395aa8b972bd725c4b

Change-Id: I719558761f370c2e29996fde4aaae647c8237001
Reviewed-on: https://chromium-review.googlesource.com/180960
Reviewed-by: Mike Frysinger <vapier@chromium.org>
Tested-by: Daniel Erat <derat@chromium.org>
Commit-Queue: Daniel Erat <derat@chromium.org>
diff --git a/platform.gyp b/platform.gyp
index afbbef4..5803931 100644
--- a/platform.gyp
+++ b/platform.gyp
@@ -6,6 +6,7 @@
       'dependencies': [
         '<(DEPTH)/libchromeos/libchromeos-<(libbase_ver).gyp:*',
         '<(DEPTH)/metrics/metrics.gyp:*',
+        '<(DEPTH)/power_manager/power_manager.gyp:*',
         '<(DEPTH)/system_api/system_api.gyp:*',
       ],
       'conditions': [