Explicitly specify whether to emit frame pointers by default.

build/config/compiler/BUILD.gn

Index: build/config/compiler/BUILD.gn
diff --git a/build/config/compiler/BUILD.gn b/build/config/compiler/BUILD.gn
index 6774b2a36b68419ac0e649da0b3292ff3e15647b..0d5953392da6bca3db282f1d413ae457f9fdd7d0 100644
--- a/build/config/compiler/BUILD.gn
+++ b/build/config/compiler/BUILD.gn
@@ -1294,7 +1294,6 @@ config("no_incompatible_pointer_warnings") {
 if (is_win) {
   common_optimize_on_cflags = [
     "/Ob2",  # Both explicit and auto inlining.
-    "/Oy-",  # Disable omitting frame pointers, must be after /O2.
     "/d2Zi+",  # Improve debugging of optimized code.
     "/Zc:inline",  # Remove unreferenced COMDAT (faster links).
   ]
@@ -1384,18 +1383,21 @@ if (is_win) {
 }
 
 config("default_stack_frames") {
-  if (is_posix && !(is_mac || is_ios)) {
-    if (using_sanitizer || enable_profiling || is_debug ||
-        current_cpu == "arm64") {
-      # Explicitly ask for frame pointers, otherwise:
-      # * Stacks may be missing for sanitizer and profiling builds.
-      # * Debug tcmalloc can crash (crbug.com/636489).
-      # * Stacks may be missing for arm64 crash dumps (crbug.com/391706).
+  if (is_posix) {
+    if (emit_frame_pointers_by_default) {

[Primiano Tucci (use gerrit), 2017/03/30 13:15:03]

(Just some naming bikeshedding)
1. by_default
just a small thought, I personally always found hard to reason on variables
called "do_something_by_default" because I can never tell if the semantic is:
- by default, do something (but in this case, why do we have a variable?)
- do something for all targets, unless a target opts out.

I suppose, this is the case for the latter. If that is the case, why not just
calling this "emit_frame_pointers" ?

2. "emit" vs "omit":
 Unfortunately, people got used to reason on frame pointers in negative logic,
because the compiler flag is called -f(no)-omit-frame-pointer. I'm always up for
using positive logic, but calling this "emit" might confuse a distract reader.

How about calling this just "enabled_frame_pointers"? It would be aligned with
the various enable_XXX that we have in build files.

[erikchen, 2017/03/30 22:12:47]

Done.

       cflags = [ "-fno-omit-frame-pointer" ]
-    } else if (is_android) {
+    } else {
       cflags = [ "-fomit-frame-pointer" ]
     }
   }
+
+  if (is_win) {
+    if (emit_frame_pointers_by_default) {
+      common_optimize_on_cflags += [ "/Oy-" ]  # Disable omitting frame pointers, must be after /O2.
+    } else {
+      common_optimize_on_cflags += [ "/Oy" ]
+    }
+  }
 }
 
 # Default "optimization on" config.