Content "gn check" work.

Make content/gpu and content/plugin pass GN check. Significant work for most of content/test

Makes most of content/shell and content/test pass check. These are not all enabled yet pending a few remaining issues that are more difficult to solve.

The private content targets now allow content/test to include headers from them for non-component builds. Checking is disabled for content/test in component builds as described in the comment at the top of //content/BUILD.gn

Renames the ui/events/ipc according to GN style.

Annotates all content and gpu visibility declarations with why the're there, and fixes some incorrect ones that people added without understanding.

Reland of https://codereview.chromium.org/1828483002/ with significant changes.
TBR=jschuh (non-security-sensitive ipc build changes)

Review URL: https://codereview.chromium.org/1833193002

Cr-Commit-Position: refs/heads/master@{#383358}

7 files changed, 18 insertions, 2 deletions

diff --git a/content/public/browser/BUILD.gn b/content/public/browser/BUILD.gn
index 643cb8f..5b04b1e 100644
--- a/content/public/browser/BUILD.gn
+++ b/content/public/browser/BUILD.gn
@@ -19,6 +19,7 @@ group("browser") {
 }
 
 source_set("browser_sources") {
+  # External code should depend on via ":browser" above.
   visibility = [ "//content/*" ]
 
   sources = rebase_path(content_browser_gypi_values.public_browser_sources,
@@ -40,7 +41,7 @@ source_set("browser_sources") {
   ]
   deps = [
     "//cc",
-    "//content/browser",
+    "//content/browser",  # Must not be public_deps!
     "//content/public/common:common_sources",
     "//gpu",
     "//media",
diff --git a/content/public/child/BUILD.gn b/content/public/child/BUILD.gn
index 6573af8..68c9986 100644
--- a/content/public/child/BUILD.gn
+++ b/content/public/child/BUILD.gn
@@ -24,6 +24,7 @@ group("child") {
 }
 
 source_set("child_sources") {
+  # External code should depend in via ":child" above.
   visibility = [ "//content/*" ]
 
   sources = rebase_path(content_child_gypi_values.public_child_sources,
diff --git a/content/public/common/BUILD.gn b/content/public/common/BUILD.gn
index 39a95fd..02712fe 100644
--- a/content/public/common/BUILD.gn
+++ b/content/public/common/BUILD.gn
@@ -78,6 +78,7 @@ source_set("static_switches") {
 }
 
 source_set("common_sources") {
+  # External code should depend on via ":common" above.
   visibility = [ "//content/*" ]
 
   sources = rebase_path(content_common_gypi_values.public_common_sources,
diff --git a/content/public/gpu/BUILD.gn b/content/public/gpu/BUILD.gn
index 63550aa..fa0be53 100644
--- a/content/public/gpu/BUILD.gn
+++ b/content/public/gpu/BUILD.gn
@@ -16,6 +16,8 @@ group("gpu") {
 }
 
 source_set("gpu_sources") {
+  # You must depend on this via //content/public/gpu above for the component
+  # build to work properly.
   visibility = [ "//content/*" ]
 
   configs += [ "//content:content_implementation" ]
@@ -30,4 +32,6 @@ source_set("gpu_sources") {
     "//content/gpu:gpu_sources",
     "//content/public/common:common_sources",
   ]
+
+  allow_circular_includes_from = [ "//content/gpu:gpu_sources" ]
 }
diff --git a/content/public/plugin/BUILD.gn b/content/public/plugin/BUILD.gn
index e4c4d36..1693b4e 100644
--- a/content/public/plugin/BUILD.gn
+++ b/content/public/plugin/BUILD.gn
@@ -16,6 +16,7 @@ group("plugin") {
 }
 
 source_set("plugin_sources") {
+  # External code should depend on via ":plugin" above.
   visibility = [ "//content/*" ]
 
   sources = [
@@ -24,7 +25,13 @@ source_set("plugin_sources") {
 
   deps = [
     "//base",
-    "//content/plugin",
+    "//content/plugin",  # Must not be a public dep.
     "//content/public/common:common_sources",
   ]
+
+  allow_circular_includes_from = [
+    # This target is a pair with content/plugin. They always go together and
+    # include headers from each other.
+    "//content/plugin",
+  ]
 }
diff --git a/content/public/renderer/BUILD.gn b/content/public/renderer/BUILD.gn
index c31a7bb..c0eaab1 100644
--- a/content/public/renderer/BUILD.gn
+++ b/content/public/renderer/BUILD.gn
@@ -19,6 +19,7 @@ group("renderer") {
 }
 
 source_set("renderer_sources") {
+  # External code should depend on via ":renderer" above.
   visibility = [ "//content/*" ]
 
   sources = rebase_path(content_renderer_gypi_values.public_renderer_sources,
diff --git a/content/public/utility/BUILD.gn b/content/public/utility/BUILD.gn
index c9fce03..c0e514c 100644
--- a/content/public/utility/BUILD.gn
+++ b/content/public/utility/BUILD.gn
@@ -18,6 +18,7 @@ group("utility") {
 }
 
 source_set("utility_sources") {
+  # External code should depend on via ":utility" above.
   visibility = [ "//content/*" ]
 
   sources = rebase_path(content_utility_gypi_values.public_utility_sources,