Make strip_absolute_paths_from_debug_symbols default to true on macOS.

This makes goma cache hits more likely.

This will break debugging unless people follow the new instrucitons at
https://chromium.googlesource.com/chromium/src/+/HEAD/docs/lldbinit.md. The test
runner now prints a message pointing to the new instructions, and I'll send an
email heads-up to chromium-dev once this lands.

This has no effect if enable_dsym is set, so this doesn't affect official
builds.

Bug: 330262
Change-Id: I1d829215f1a8ff3d4f071959e7c0364011799519
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1774272
Commit-Queue: Erik Chen <erikchen@chromium.org>
Reviewed-by: Nico Weber <thakis@chromium.org>
Auto-Submit: Erik Chen <erikchen@chromium.org>
Cr-Commit-Position: refs/heads/master@{#691845}

build/config/compiler/compiler.gni

@@ -23,6 +23,10 @@ if (current_cpu == "arm" || current_cpu == "arm64") {
   import("//build/config/arm.gni")
 }
 
+if (is_mac) {
+  import("//build/config/mac/symbols.gni")
+}
+
 declare_args() {
   # How many symbols to include in the build. This affects the performance of
   # the build since the symbols are large and dealing with them is slow.
@@ -197,8 +201,13 @@ declare_args() {
   # in turn is important for goma compile hit rate.
   # Setting this to true may make it harder to debug binaries on Linux, see
   # https://chromium.googlesource.com/chromium/src/+/master/docs/linux_debugging.md#Source-level-debug-with-fdebug_compilation_dir
+  # It's not clear if the crash server will correctly handle dSYMs with relative
+  # paths, so we disable this feature for official benefit. The main benefit is
+  # deterministic builds to reduce compile times, so this is less relevant for
+  # official builders.
   strip_absolute_paths_from_debug_symbols =
-      is_android || is_fuchsia || is_nacl || (is_win && use_lld) || is_linux
+      is_android || is_fuchsia || is_nacl || (is_win && use_lld) || is_linux ||
+      (is_mac && !enable_dsyms)
 }
 
 # If it wasn't manually set, set to an appropriate default.

docs/lldbinit.md

@@ -2,7 +2,7 @@
 
 Usage of Chromium's [lldbinit.py](../tools/lldb/lldbinit.py) is recommended when
 debugging with lldb. This is necessary for source-level debugging when
-`strip_absolute_paths_from_debug_symbols` is enabled.
+`strip_absolute_paths_from_debug_symbols` is enabled [this is the default].
 
 To use, add the following to your `~/.lldbinit`