Only build CupsProxyService internals w/ libCUPS

Currently breaking a veyron build, bug linked below, since SocketManager
is built regardless of libCUPS, but still technically depends on the
kHttpMaxBufferSize constant in cups_proxy/public/cpp/cups_util.

Though we could bring the constant to the SocketManager internals, there
is no clear reason for SocketManager to be built this way so this just brings it in line with the rest of the service internals..

TBR=rockot@chromium.org,skau@chromium.org

Bug: chromium:971906
Test: tests still pass && speculative build-breaking fix
Change-Id: Ic9b873093152c4bff01ed940551db2cdf36605c3
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1648747
Commit-Queue: Luum Habtemariam <luum@chromium.org>
Reviewed-by: Achuith Bhandarkar <achuith@chromium.org>
Cr-Commit-Position: refs/heads/master@{#667296}

chrome/services/cups_proxy/BUILD.gn

@@ -14,8 +14,6 @@ source_set("cups_proxy") {
     "cups_proxy_service.h",
     "cups_proxy_service_delegate.cc",
     "cups_proxy_service_delegate.h",
-    "socket_manager.cc",
-    "socket_manager.h",
   ]
 
   deps = [
@@ -34,6 +32,8 @@ source_set("cups_proxy") {
     sources += [
       "printer_installer.cc",
       "printer_installer.h",
+      "socket_manager.cc",
+      "socket_manager.h",
     ]
   }
 
@@ -57,23 +57,23 @@ static_library("test_support") {
 source_set("unit_tests") {
   testonly = true
 
-  sources = [
-    "socket_manager_unittest.cc",
-  ]
+  # Target is empty unless libCUPS is available.
+  if (use_cups) {
+    sources = [
+      "printer_installer_unittest.cc",
+      "socket_manager_unittest.cc",
+    ]
 
-  deps = [
-    ":cups_proxy",
-    ":test_support",
-    "//base",
-    "//chrome/services/cups_proxy/public/cpp",
-    "//testing/gtest",
-  ]
+    deps = [
+      ":cups_proxy",
+      ":test_support",
+      "//base",
+      "//chrome/services/cups_proxy/public/cpp",
+      "//testing/gtest",
+    ]
 
-  if (use_cups) {
-    sources += [ "printer_installer_unittest.cc" ]
+    data = [
+      "//chrome/test/data/cups_proxy",
+    ]
   }
-
-  data = [
-    "//chrome/test/data/cups_proxy",
-  ]
 }