[Build] Add an 'is_unsafe_developer_build' gn argument.

- Adds an UNSAFE_DEVELOPER_BUILD flag too.

Bug: chromium:756050
Change-Id: I17bf8fcfb331f3fa11541fed64e9dae48a1c529f
Reviewed-on: https://chromium-review.googlesource.com/714443Reviewed-by: Dirk Pranke <dpranke@chromium.org>
Reviewed-by: Lei Zhang <thestig@chromium.org>
Commit-Queue: Bill Budge <bbudge@chromium.org>
Cr-Commit-Position: refs/heads/master@{#509528}

base/BUILD.gn

@@ -45,6 +45,11 @@ declare_args() {
   # (file, function, line). False means only the program counter (and currently
   # file name) is saved.
   enable_location_source = true
+
+  # Unsafe developer build. Has developer-friendly features that may weaken or
+  # disable security measures like sandboxing or ASLR.
+  # IMPORTANT: Unsafe developer builds should never be distributed to end users.
+  is_unsafe_developer_build = !is_official_build
 }
 
 if (is_android) {
@@ -1694,6 +1699,7 @@ buildflag_header("debugging_flags") {
     "ENABLE_LOCATION_SOURCE=$enable_location_source",
     "ENABLE_PROFILING=$enable_profiling",
     "CAN_UNWIND_WITH_FRAME_POINTERS=$can_unwind_with_frame_pointers",
+    "UNSAFE_DEVELOPER_BUILD=$is_unsafe_developer_build",
   ]
 }
 

build/config/BUILD.gn

@@ -49,7 +49,7 @@ declare_args() {
 # and means its definition can participate in the build graph, only recompiling
 # things when it actually changes.
 #
-# See //build/buildflag_header.gni for inntructions on generating headers.
+# See //build/buildflag_header.gni for instructions on generating headers.
 #
 # This will also allow you to scope your build flag to a BUILD.gn file (or a
 # .gni file if you need it from more than one place) rather than making global