Version: ToT 04/13/2016
OS: OS X

What steps will reproduce the problem?
(1) Generate a new gn folder, say gn args out/gnasan 
(2) Configure for asan build (but I don't think this matters), i.e.

is_asan = true
enable_nacl = false  # Necessary until NaCl GN build is more complete.
is_debug = false  # Release build.

(3) Run ninja -C out/gnasan blink_platform_unittests

What is the expected output?

Builds and links successfully.

What do you see instead?

In file included from ../../third_party/WebKit/Source/modules/bluetooth/BluetoothRemoteGATTService.cpp:12:
In file included from ../../third_party/WebKit/Source/modules/bluetooth/BluetoothError.h:9:
../../third_party/WebKit/public/platform/modules/bluetooth/WebBluetoothError.h:8:10: fatal error: 'public/platform/modules/bluetooth/web_bluetooth.mojom.h' file not found
#include "public/platform/modules/bluetooth/web_bluetooth.mojom.h"
         ^

When I add "chrome" as a build target, everything completes and the header is generated from the mojom file. I am guessing there is a missing dependency to the mojo code generation somewhere?