Use the /PROFILE linker flag for the Windows GN builds.

build/config/win/BUILD.gn

Index: build/config/win/BUILD.gn
diff --git a/build/config/win/BUILD.gn b/build/config/win/BUILD.gn
index e8039c0b1f75eb628f2c419bbe2aebf8de9f32d6..9188a081eb350894c7c63aaf7281ade93b07138b 100644
--- a/build/config/win/BUILD.gn
+++ b/build/config/win/BUILD.gn
@@ -96,9 +96,11 @@ config("compiler") {
     lib_dirs = [ "//third_party/llvm-build/Release+Asserts/lib/clang/$clang_version/lib/windows" ]
   }
 
-  if (is_syzyasan) {
-    # SyzyAsan needs /PROFILE turned on to produce appropriate pdbs.
-    assert(!is_win_fastlink, "/PROFILE and /DEBUG:FASTLINK are incompatible")
+  # Ensures that the PDB file contains FIXUP information (growing the PDB file
+  # by about 5%) but does not otherwise alter the output binary. This
+  # information is used by the Syzygy optimization tool when decomposing the
+  # release image.
+  if (!is_debug && !is_win_fastlink && !is_clang) {

[brucedawson, 2016/06/21 21:28:49]

I didn't notice is_clang checks in the GYP version of this setting, although the
PROFILE settings were pretty well spread out so I can't be sure. Is the is_clang
check appropriate?

Also, do we want /PROFILE on non-syzyasan builds?

Also, there has been some discussion of turning on incremental linking for
release component builds, and incremental linking is incompatible with /PROFILE.

Just checking to make sure we have the right cases. It sounds like generating
the FIXUP information is not free so we might as well do it as rarely as
possible. I only noticed build breaks from the lack of this on official builds,
FWIW.

[Sébastien Marchand, 2016/06/22 14:59:47]

There's no 'is_clang' check in the GYP version of this setting but this is
probably a mistake as we don't plan to support the Clang builds (what we're
doing with Syzygy doesn't really make sense with Clang).

We should keep in mind that we'll need to add an additional check the day we'll
turn on incremental linking for the release component builds (there's not so
much we can do until then). 

Generating the FIXUP information only affect the PDB (for a 5% increase in
size), and I think that keeping the ability to instrument (with SyzyAsan or for
Coverage) 'any' Chrome build without rebuilding is worth this extra cost ? 

     ldflags = [ "/PROFILE" ]
   }