Rework default GN symbol handling for win goma builds.

build/config/compiler/compiler.gni

 # Copyright 2015 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 import("//build/config/android/config.gni")
 import("//build/config/chrome_build.gni")
 import("//build/config/chromecast_build.gni")
 import("//build/config/sanitizers/sanitizers.gni")
 import("//build/toolchain/toolchain.gni")
 
@@ skipping 64 matching lines @@
                               current_cpu == "arm")))
 }
 
 # If it wasn't manually set, set to an appropriate default.
 assert(symbol_level >= -1 && symbol_level <= 2, "Invalid symbol_level")
 if (symbol_level == -1) {
   if (is_android && use_order_profiling) {
     # With instrumentation enabled, debug info puts libchrome.so over 4gb, which
     # causes the linker to produce an invalid ELF. http://crbug.com/574476
     symbol_level = 0
+  } else if (is_win && use_goma) {
+    # goma doesn't support PDB files, so we disable symbols during goma
+    # compilation because otherwise the redundant debug information

[Nico, 2016/08/03 23:42:16]

Don't we want this for non win too?

[Dirk Pranke, 2016/08/03 23:54:36]

I'm not sure what you're asking.

goma + full symbols works fine (though slower) on the other platforms, so
we don't *have* to do this change. And, I believe there are a fair number of
people that build locally with full symbols + goma on at least linux. So, I
don't think we should prohibit goma+full_symbols on mac/linux/android/ios.

Are you asking whether we should change the default so that non-win
release builds also pick up minimal symbols?

These days, most (non-win) trybots are explicitly set to minimal_symbols, but
release
waterfall builds pick up the defaults (so, full symbols on mac, no symbols on
linux).

We can change things so that releases default to minimal_symbols; 
it would make stack traces worse on mac but possibly speed up cycle times, and 
it would slow build times on linux (locally, and on waterfall linux builders)
for 
waterfall linux builders. But, it would make things a lot more consistent.

So, making that change might be better done in a separate CL so we can isolate
the effects on cycle times and load better. 

+    # (repeated in every .obj file) makes linker memory consumption and
+    # link times unsustainable (crbug.com/630074).
+    symbol_level = 1
   } else if (is_win && is_clang && !using_sanitizer) {
     # TODO(thakis): Remove this again once building with clang/win and
     # debug info doesn't make link.exe run for hours.
     symbol_level = 1
   } else if (!is_linux || is_debug || is_official_build || is_chromecast) {
     # Linux is slowed by having symbols as part of the target binary, whereas
     # Mac and Windows have them separate, so in Release Linux, default them off,
     # but keep them on for Official builds and Chromecast builds.
     symbol_level = 2
   } else if (using_sanitizer) {
     # Sanitizers require symbols for filename suppressions to work.
     symbol_level = 1
   } else {
     symbol_level = 0
   }
 }