Update component build documentation.

build/config/BUILDCONFIG.gn

Index: build/config/BUILDCONFIG.gn
diff --git a/build/config/BUILDCONFIG.gn b/build/config/BUILDCONFIG.gn
index 8c565aa6418a00f025a01f8508fa06dc17aaf9bb..e539df782cf46bcc527cea20f969f3faf5031d62 100644
--- a/build/config/BUILDCONFIG.gn
+++ b/build/config/BUILDCONFIG.gn
@@ -144,6 +144,9 @@ declare_args() {
   # Component build. Setting to true compiles targets declared as "components"
   # as shared libraries loaded dynamically. This speeds up development time.
   # When false, components will be linked statically.
+  #
+  # For more information see
+  # https://chromium.googlesource.com/chromium/src/+/master/docs/component_build.md

[Dirk Pranke, 2016/08/04 15:59:04]

I'm tempted to say that this should be "//docs/component_build.md" or
"../../docs/component_build.md" instead, but neither of those gives you a
clickable link, so I'm not really sure they're improvements.

[brettw, 2016/08/04 18:26:41]

I considered that, but decided most people will prefer to read on the web than
in raw markdown form.

   is_component_build = is_debug && current_os != "ios"
 }