Reland of Setting is_component_build to false by default (patchset #1 id:1 of https://codereview.webrtc.org/2731703004/ )

Reason for revert:
Trying to fix this skipping the check if we are building webrtc within chromium.

Original issue's description:
> Revert of Setting is_component_build to false by default (patchset #5 id:80001 of https://codereview.webrtc.org/2728643003/ )
>
> Reason for revert:
> Breaks chrome rolls
>
> Original issue's description:
> > Setting is_component_build to false by default
> >
> > Webrtc does not support component builds so we want to override
> > the chromium default value (which can be true on debug builds if the
> > os is different from iOS).
> >
> > Please note that the user can set this value to true in two ways:
> >
> >  - using --args (e.g.: gn gen out/default --args='is_component_build=true'
> >  - changing the value in the args.gn file
> >
> > But in both cases the value will be ignored because we don't use the
> > 'component' template but we rely directly on 'rtc_static_library' and
> > 'rtc_shared_library'.
> >
> > BUG=webrtc:6975
> > NOTRY=True
> >
> > Review-Url: https://codereview.webrtc.org/2728643003
> > Cr-Commit-Position: refs/heads/master@{#17020}
> > Committed: https://chromium.googlesource.com/external/webrtc/+/2cb3944ba7e4467601ebd94888e1811a6d77be49
>
> TBR=kjellander@webrtc.org,mbonadei@webrtc.org
> # Skipping CQ checks because original CL landed less than 1 days ago.
> NOPRESUBMIT=true
> NOTREECHECKS=true
> NOTRY=true
> BUG=webrtc:6975
>
> Review-Url: https://codereview.webrtc.org/2731703004
> Cr-Commit-Position: refs/heads/master@{#17025}
> Committed: https://chromium.googlesource.com/external/webrtc/+/2d9e7685a59c05e62c23d7125064c8e5c1f88edb

TBR=kjellander@webrtc.org,tommi@webrtc.org
# Skipping CQ checks because original CL landed less than 1 days ago.
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=webrtc:6975

Review-Url: https://codereview.webrtc.org/2729243003
Cr-Commit-Position: refs/heads/master@{#17027}
diff --git a/.gn b/.gn
index 2070fa8..547ca84 100644
--- a/.gn
+++ b/.gn
@@ -51,3 +51,14 @@
 # to force additional review for new uses of exec_script, which is strongly
 # discouraged except for gypi_to_gn calls.
 exec_script_whitelist = build_dotfile_settings.exec_script_whitelist
+
+default_args = {
+  # Webrtc does not support component builds because we are not using the
+  # template "component" but we rely directly on "rtc_static_library" and
+  # "rtc_shared_library". This means that we cannot use the chromium default
+  # value for this argument.
+  # This also means that the user can override this value using --args or
+  # the args.gn file but this setting will be ignored because we don't support
+  # component builds.
+  is_component_build = false
+}