Rework default GN symbol handling for win goma builds.

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 79723f6cc76c041697955f5c7de91e2935e78aa5..984a4e3b63e6de45bc9de24f498c9f0e531a632c 100644
--- a/build/config/compiler/BUILD.gn
+++ b/build/config/compiler/BUILD.gn
@@ -1484,14 +1484,8 @@ config("default_optimization") {
 config("symbols") {
   if (is_win) {
     import("//build/toolchain/goma.gni")
-    if (use_goma) {
-      # Disable symbols during goma compilation because otherwise the redundant
-      # debug information (repeated in every .obj file) makes linker memory
-      # consumption and link times unsustainable (crbug.com/630074).
-      cflags = []
-    } else {
-      cflags = [ "/Zi" ]  # Produce PDB file, no edit and continue.
-    }
+    cflags = [ "/Zi" ]  # Produce PDB file, no edit and continue.
+
     if (is_win_fastlink && visual_studio_version != "2013") {
       # Tell VS 2015+ to create a PDB that references debug
       # information in .obj and .lib files instead of copying
@@ -1560,6 +1554,11 @@ config("default_symbols") {
   } else if (symbol_level == 1) {
     configs = [ ":minimal_symbols" ]
   } else if (symbol_level == 2) {
+    assert(
+        !(is_win && use_goma),

[Reid Kleckner, 2016/08/13 01:55:27]

I'd like it if you tossed in '&& !is_clang' so that you can build with
'is_clang=true use_goma=true symbol_level=2' and get a full symbols.

Goma will not make linking clang-built objects any slower or faster, since clang
aliases /Zi to /Z7. Our link times with /Z7 aren't particularly good, but they
aren't as bad as MSVC's, probably because we emit less stuff.

[Dirk Pranke, 2016/08/14 23:34:58]

Okay, will do.

At the moment, I'm actually leaning to removing the assert altogether and seeing
what happens.

+        "Cannot generate full symbols on windows with goma, use " +
+            "symbol_level=1 or compile locally without goma, which will be " +
+            "faster anyway.")
     configs = [ ":symbols" ]
   } else {
     assert(false)