Define crash keys in the directory hierarchy where they are used.

content/public/common/BUILD.gn

Index: content/public/common/BUILD.gn
diff --git a/content/public/common/BUILD.gn b/content/public/common/BUILD.gn
index 9432838d266fc701951510df089ff87648cdd8d5..100e02583dc861ca2698e3027965b1f9112455ac 100644
--- a/content/public/common/BUILD.gn
+++ b/content/public/common/BUILD.gn
@@ -77,6 +77,24 @@ source_set("static_switches") {
   public_configs = [ ":static_switches_defines" ]
 }
 
+# This target allows you to use the crash_keys constants (and registration
+# function) without depending on the rest of content.
+source_set("crash_keys") {
+  public = [
+    "crash_keys.h",
+  ]
+  sources = [
+    "//content/common/content_export.h",
+    "crash_keys.cc",
+  ]
+  deps = [
+    "//base",
+    "//components/crash/core/common",
+  ]
+
+  public_configs = [ "//content:content_implementation" ]
+}
+
 source_set("common_sources") {
   # External code should depend on via ":common" above.
   visibility = [ "//content/*" ]
@@ -101,6 +119,7 @@ source_set("common_sources") {
     "//url/ipc:url_ipc",
   ]
   deps = [
+    "//components/crash/core/common",
     "//ipc",
     "//media",
     "//mojo/common",