Make debug builds component builds by default.

build/config/BUILDCONFIG.gn

 # Copyright (c) 2013 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 # =============================================================================
 # PLATFORM SELECTION
 # =============================================================================
 #
 # There are two main things to set: "os" and "cpu". The "toolchain" is the name
 # of the GN thing that encodes combinations of these things.
@@ skipping 61 matching lines @@
 # you can just declare it in the corresponding BUILD.gn file. If you need a
 # flag in multiple components, there are a few options:
 #
 # - If your feature is a single target, say //components/foo, and the targets
 #   depending on foo need to have some define set if foo is enabled: (1) Write
 #   a declare_args block in foo's BUILD.gn file listing your enable_foo build
 #   flag. (2) Write a config in that file listing the define, and list that
 #   config in foo's public_configs. This will propagate that define to all the
 #   targets depending on foo. (3) When foo is not enabled, just make it expand
 #   to an empty group (or whatever's appropriate for the "off" state of your
-#   feature.
+#   feature).
 #
 # - If a semi-random set of targets need to know about a define: (1) In the
 #   lowest level of the build that knows about this feature, add a declare_args
 #   block in the build file for your enable flag. (2) Write a config that adds
 #   a define conditionally based on that build flags. (3) Manually add that
 #   config to the "configs" applying to the targets that need the define.
 #
 # - If a semi-random set of targets need to know about the build flag (to do
 #   file inclusion or exclusion, more than just defines): (1) Write a .gni file
 #   in the lowest-level directory that knows about the feature. (2) Put the
@@ skipping 11 matching lines @@
 # - Use a name like "use_foo" or "is_foo" (whatever is more appropriate for
 #   your feature) rather than just "foo".
 #
 # - Write good comments directly above the declaration with no blank line.
 #   These comments will appear as documentation in "gn args --list".
 #
 # - Don't call exec_script inside declare_args. This will execute the script
 #   even if the value is overridden, which is wasteful. See first bullet.
 
 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.
-  is_component_build = false
-
   # Set to enable the official build level of optimization. This has nothing
   # to do with branding, but enables an additional level of optimization above
   # release (!is_debug). This might be better expressed as a tri-state
   # (debug, release, official) but for historical reasons there are two
   # separate flags.
   is_official_build = false
 
   # Debug build. Enabling official builds automatically sets is_debug to false.
   is_debug = !is_official_build
 
   # Whether we're a traditional desktop unix.
   is_desktop_linux = current_os == "linux"
 
   # Set to true when compiling with the Clang compiler. Typically this is used
   # to configure warnings.
   is_clang = current_os == "mac" || current_os == "ios" ||
              current_os == "linux" || current_os == "chromeos"
 
   # Allows the path to a custom target toolchain to be injected as a single
   # argument, and set as the default toolchain.
   custom_toolchain = ""
 
   # This should not normally be set as a build argument.  It's here so that
   # every toolchain can pass through the "global" value via toolchain_args().
   host_toolchain = ""
 
   # DON'T ADD MORE FLAGS HERE. Read the comment above.
 }
 
+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.
+  is_component_build = is_debug && current_os != "ios"
+}
+
 assert(!(is_debug && is_official_build), "Can't do official debug builds")
 
 # ==============================================================================
 # TOOLCHAIN SETUP
 # ==============================================================================
 #
 # Here we set the default toolchain, as well as the variable host_toolchain
 # which will identify the toolchain corresponding to the local system when
 # doing cross-compiles. When not cross-compiling, this will be the same as the
 # default toolchain.
@@ skipping 472 matching lines @@
 set_defaults("component") {
   if (is_component_build) {
     configs = default_shared_library_configs
     if (is_android) {
       configs -= [ "//build/config/android:hide_native_jni_exports" ]
     }
   } else {
     configs = default_compiler_configs
   }
 }