Fix compilation failure when v8 is compiled with Chromium using GYP.

Compilation breaks when compiling v8 through Chromium using GYP. The isssue
started to appear after https://codereview.chromium.org/2190973003 landed.
It happens because trace_event_common.h header is on different location if we
are compiling v8 through Chromium compared to when we are compiling v8 standalone.

BUG=

Review-Url: https://codereview.chromium.org/2207943002
Cr-Commit-Position: refs/heads/master@{#38333}

src/v8.gyp

@@ -2003,6 +2003,7 @@
       ],
       'include_dirs+': [
         '..',
+        '<(DEPTH)',
         '../include',
       ],
       'sources': [