Disable Warning 4702 for the PGO builds.

build/common.gypi

Index: build/common.gypi
diff --git a/build/common.gypi b/build/common.gypi
index 5a2753f08af3172e7c9d25e2efb04e6479d74aad..fe22c66aa14abb0b2cec5e4f9028859afd5717fe 100644
--- a/build/common.gypi
+++ b/build/common.gypi
@@ -4967,6 +4967,14 @@
                   },
                 ],
                 ['optimize=="max"', {
+                    # Disable Warning 4702 ("Unreachable code") for the WPO/PGO
+                    # builds. Probably anything that this would catch that
+                    # wouldn't be caught in a normal build isn't going to
+                    # actually be a bug, so the incremental value of C4702 for
+                    # PGO builds is likely very small.
+                    'msvs_disabled_warnings': [
+                      4702

[bradn, 2014/06/10 16:42:47]

Could you not introduce a define here to allow the unreached markers in question
to be gated out only in this context?

[Sébastien Marchand, 2014/06/10 17:03:33]

I could do this, but maintaining a list of these would be pretty painful... The
PGO build process takes hours and crash as soon as one of these warning is
encountered, so we'll have to spend hours trying to find the lines that trigger
this warning for no real value... See crbug.com/380175 for the discussion we had
about this with pkasting@ and scottmg@

+                    ],
                     'msvs_settings': {
                       'VCCLCompilerTool': {
                         # 2, optimizeMaxSpeed, Maximize Speed (/O2)