<third_party/WebKit> Add missing dependency to khronos_headers

This is needed since https://codereview.chromium.org/106503003
and because of our chromium patch that fixes the build with a
GL ES2 configured Qt.

Change-Id: I2dfa1afe1bb58227656fee798a5d2549f88c3f9d
Reviewed-by: Zeno Albisser <[email protected]>

Author: bbandix

chromium/third_party/WebKit/Source/core/core.gyp

@@ -821,6 +821,7 @@
         'webcore_derived',
         '../wtf/wtf.gyp:wtf',
         '<(DEPTH)/skia/skia.gyp:skia',
+        '<(DEPTH)/third_party/khronos/khronos.gyp:khronos_headers',
         '<(DEPTH)/third_party/npapi/npapi.gyp:npapi',
         '<(DEPTH)/third_party/qcms/qcms.gyp:qcms',
         '<(DEPTH)/url/url.gyp:url_lib',
@@ -830,6 +831,7 @@
         '../wtf/wtf.gyp:wtf',
         'webcore_derived',
         '<(DEPTH)/skia/skia.gyp:skia',
+        '<(DEPTH)/third_party/khronos/khronos.gyp:khronos_headers',
         '<(DEPTH)/third_party/npapi/npapi.gyp:npapi',
         '<(DEPTH)/third_party/qcms/qcms.gyp:qcms',
         '<(DEPTH)/url/url.gyp:url_lib',