1--- a/build/build_config.h
2+++ b/build/build_config.h
3@@ -16,6 +16,40 @@
4 #ifndef BUILD_BUILD_CONFIG_H_
5 #define BUILD_BUILD_CONFIG_H_
6
7+// A brief primer on #defines:
8+//
9+// - __ANDROID__ is automatically defined by the Android toolchain (see
10+//   https://goo.gl/v61lXa). It's not defined when building host code.
11+// - __ANDROID_HOST__ is defined via -D by Android.mk when building host code
12+//   within an Android checkout.
13+// - ANDROID is defined via -D when building code for either Android targets or
14+//   hosts. Use __ANDROID__ and __ANDROID_HOST__ instead.
15+// - OS_ANDROID is a Chrome-specific define used to build Chrome for Android
16+//   within the NDK.
17+
18+// Android targets and hosts don't use tcmalloc.
19+#if defined(__ANDROID__) || defined(__ANDROID_HOST__)
20+#define NO_TCMALLOC
21+#endif  // defined(__ANDROID__) || defined(__ANDROID_HOST__)
22+
23+// Use the Chrome OS version of the code for both Android targets and Chrome OS builds.
24+#if !defined(__ANDROID_HOST__)
25+#define OS_CHROMEOS 1
26+#endif  // !defined(__ANDROID_HOST__)
27+
28+#if defined(__ANDROID__)  // Android targets
29+
30+#define __linux__ 1
31+
32+#elif !defined(__ANDROID_HOST__)  // Chrome OS
33+
34+// TODO: Remove these once the GLib MessageLoopForUI isn't being used:
35+// https://crbug.com/361635
36+#define USE_GLIB 1
37+#define USE_OZONE 1
38+
39+#endif  // defined(__ANDROID__)
40+
41 // A set of macros to use for platform detection.
42 #if defined(__native_client__)
43 // __native_client__ must be first, so that other OS_ defines are not set.
44@@ -28,8 +62,7 @@
45 #else
46 #define OS_NACL_SFI
47 #endif
48-#elif defined(ANDROID)
49-#define OS_ANDROID 1
50+// Don't set OS_ANDROID; it's only used when building Chrome for Android.
51 #elif defined(__APPLE__)
52 // only include TargetConditions after testing ANDROID as some android builds
53 // on mac don't have this header available and it's not needed unless the target
54