Add --dump-line-box-trees parameter to content_shell.

content/shell/renderer/layout_test/blink_test_runner.cc

Index: content/shell/renderer/layout_test/blink_test_runner.cc
diff --git a/content/shell/renderer/layout_test/blink_test_runner.cc b/content/shell/renderer/layout_test/blink_test_runner.cc
index 009f47581edc800d7cc85e50172e8b06f1e4bcaf..70b4215da24d79ae94c01c2f6a5613ddbd1d4cf4 100644
--- a/content/shell/renderer/layout_test/blink_test_runner.cc
+++ b/content/shell/renderer/layout_test/blink_test_runner.cc
@@ -781,8 +781,11 @@ void BlinkTestRunner::CaptureDump() {
     interfaces->TestRunner()->GetAudioData(&vector_data);
     Send(new ShellViewHostMsg_AudioDump(routing_id(), vector_data));
   } else {
-    Send(new ShellViewHostMsg_TextDump(routing_id(),
-                                       proxy()->CaptureTree(false)));
+      const base::CommandLine& command_line =
+          *base::CommandLine::ForCurrentProcess();
+    Send(new ShellViewHostMsg_TextDump(
+        routing_id(), proxy()->CaptureTree(
+            false, command_line.HasSwitch(switches::kDumpLineBoxTrees))));
 
     if (test_config_.enable_pixel_dumping &&
         interfaces->TestRunner()->ShouldGeneratePixelResults()) {