add --gdb-index to linker

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 b71d1464f94dc80f01ea7c74df5fb33cbc9414f8..50fc2d290bbd02d3513f21ad39c88a5b0d22280e 100644
--- a/build/config/compiler/BUILD.gn
+++ b/build/config/compiler/BUILD.gn
@@ -75,6 +75,10 @@ declare_args() {
   # Omit unwind support in official builds to save space.
   # We can use breakpad for these builds.
   exclude_unwind_tables = is_chrome_branded && is_official_build
+
+  # If true, gold linker will save symbol table inside object files.
+  # This speeds up gdb startup by 60%
+  gdb_index = is_desktop_linux && is_debug && is_component_build

[Dirk Pranke, 2016/03/24 20:20:41]

Let's just have this default to false for now and land it. We can change the
value later if need be.

[atotic1, 2016/03/25 17:11:24]

Done. New patch uploaded.

 }
 
 # Apply the default logic for these values if they were not set explicitly.
@@ -287,6 +291,10 @@ config("compiler") {
       #"-Wl,--thread-count=4",
     ]
 
+    if (gdb_index) {
+      ldflags += [ "-Wl,--gdb-index" ]
+    }
+
     if (!using_sanitizer && !(is_android && use_order_profiling)) {
       # TODO(brettw) common.gypi has this only for target toolset.
       ldflags += [ "-Wl,--icf=all" ]