GN: Fix some typos in the documentation.

BUG=

Review-Url: https://codereview.chromium.org/2616523002
Cr-Original-Commit-Position: refs/heads/master@{#441257}
Cr-Mirrored-From: https://chromium.googlesource.com/chromium/src
Cr-Mirrored-Commit: 0c1dd9de8c008dd49dfbc9c646cd87027db3d577
diff --git a/tools/gn/docs/reference.md b/tools/gn/docs/reference.md
index b62abbd..034a112 100644
--- a/tools/gn/docs/reference.md
+++ b/tools/gn/docs/reference.md
@@ -3967,7 +3967,7 @@
   This addition happens in a second phase once a target and all of its
   dependencies have been resolved. Therefore, a target will not see these
   force-added configs in their "configs" variable while the script is running,
-  and then can not be removed. As a result, this capability should generally
+  and they can not be removed. As a result, this capability should generally
   only be used to add defines and include directories necessary to compile a
   target's headers.
 
@@ -5434,7 +5434,7 @@
   This addition happens in a second phase once a target and all of its
   dependencies have been resolved. Therefore, a target will not see these
   force-added configs in their "configs" variable while the script is running,
-  and then can not be removed. As a result, this capability should generally
+  and they can not be removed. As a result, this capability should generally
   only be used to add defines and include directories necessary to compile a
   target's headers.
 
diff --git a/tools/gn/variables.cc b/tools/gn/variables.cc
index d387bae..3b60c90 100644
--- a/tools/gn/variables.cc
+++ b/tools/gn/variables.cc
@@ -416,7 +416,7 @@
   This addition happens in a second phase once a target and all of its
   dependencies have been resolved. Therefore, a target will not see these
   force-added configs in their "configs" variable while the script is running,
-  and then can not be removed. As a result, this capability should generally
+  and they can not be removed. As a result, this capability should generally
   only be used to add defines and include directories necessary to compile a
   target's headers.
 
@@ -1575,7 +1575,7 @@
   This addition happens in a second phase once a target and all of its
   dependencies have been resolved. Therefore, a target will not see these
   force-added configs in their "configs" variable while the script is running,
-  and then can not be removed. As a result, this capability should generally
+  and they can not be removed. As a result, this capability should generally
   only be used to add defines and include directories necessary to compile a
   target's headers.