Don't disable debug symbols when building with sanitizers.

build/config/sanitizers/BUILD.gn

Index: build/config/sanitizers/BUILD.gn
diff --git a/build/config/sanitizers/BUILD.gn b/build/config/sanitizers/BUILD.gn
index 36d45c1d1b6f1edf77020d965aec0f298c3fa702..7f66b7ab96d46c2c701555194d0810f5c2d0df5f 100644
--- a/build/config/sanitizers/BUILD.gn
+++ b/build/config/sanitizers/BUILD.gn
@@ -262,17 +262,18 @@ config("common_sanitizer_flags") {
   cflags_cc = []
 
   # Sanitizers need line table info for stack traces. They don't need type info
-  # or variable info, so we can leave that out to speed up the build.
+  # or variable info, so we can leave that out to speed up the build, unless we
+  # are building with full debug symbols.

[Nico, 2016/12/06 14:34:12]

this should never happen:
https://cs.chromium.org/chromium/src/build/config/sanitizers/sanitizers.gni?q...

i know that things explode if you force that on in is msan or ubsan mode at
least

[mstensho (USE GERRIT), 2016/12/06 16:36:53]

I needed it today. I had to debug a use-after free bug. Kind of hard to debug
without debug symbols, right?

[Nico, 2016/12/06 16:47:44]

So I guess you disabled that assert in the other file, yes? Maybe that comment
there should say "Uncomment this locally and also uncomment -gline-tables-only
in sanitizers/BUILD.gn" instead? Keying this off is_debug seems wrong (I often
build with release+symbols, and I also sometimes do asan-builds with printf
debugging where i really just need line tables)

   if (using_sanitizer) {
     assert(is_clang, "sanitizers only supported with clang")
-    cflags += [
-      "-gline-tables-only",
+    if (!is_debug) {
+      cflags += [ "-gline-tables-only" ]
+    }
 
-      # Column info in debug data confuses Visual Studio's debugger, so don't
-      # use this by default.  However, clusterfuzz needs it for good attribution
-      # of reports to CLs, so turn it on there.
-      "-gcolumn-info",
-    ]
+    # Column info in debug data confuses Visual Studio's debugger, so don't
+    # use this by default.  However, clusterfuzz needs it for good attribution
+    # of reports to CLs, so turn it on there.
+    cflags += [ "-gcolumn-info" ]
   }
 
   # Common options for AddressSanitizer, LeakSanitizer, ThreadSanitizer,