Adding Navigation Throttles to DevTools

content/browser/devtools/render_frame_devtools_agent_host.cc

Index: content/browser/devtools/render_frame_devtools_agent_host.cc
diff --git a/content/browser/devtools/render_frame_devtools_agent_host.cc b/content/browser/devtools/render_frame_devtools_agent_host.cc
index a22158bbfd509b7e5500cdf0b570b68ae76ca881..3307123c0c594ba4508845ffbca22c22ce1cd9b0 100644
--- a/content/browser/devtools/render_frame_devtools_agent_host.cc
+++ b/content/browser/devtools/render_frame_devtools_agent_host.cc
@@ -13,6 +13,7 @@
 #include "content/browser/child_process_security_policy_impl.h"
 #include "content/browser/devtools/devtools_frame_trace_recorder.h"
 #include "content/browser/devtools/devtools_protocol_handler.h"
+#include "content/browser/devtools/page_navigation_throttle.h"
 #include "content/browser/devtools/protocol/browser_handler.h"
 #include "content/browser/devtools/protocol/dom_handler.h"
 #include "content/browser/devtools/protocol/emulation_handler.h"
@@ -345,6 +346,25 @@ void RenderFrameDevToolsAgentHost::OnBeforeNavigation(
     agent_host->AboutToNavigate(navigation_handle);
 }
 
+// static
+std::unique_ptr<NavigationThrottle>
+RenderFrameDevToolsAgentHost::GetThrottleForNavigation(
+    NavigationHandle* navigation_handle) {
+  // NOTE a single throttle registered by Page.setControlNavigations is intended

[nasko, 2016/07/13 22:37:34]

This comment is not entirely correct. Each navigation is 1:1 with
NavigationHandle and in turn NavigationHandle is associated with a
NavigationThrottle. One throttle cannot handle multiple navigations. 

[alex clarke (OOO till 29th), 2016/07/14 16:06:05]

Acknowledged.

+  // to control navigations in the main frame and all child frames.
+  FrameTreeNode* frame_tree_node =
+      static_cast<NavigationHandleImpl*>(navigation_handle)->frame_tree_node();
+  while (frame_tree_node && frame_tree_node->parent()) {
+    frame_tree_node = frame_tree_node->parent();
+  }
+  RenderFrameDevToolsAgentHost* agent_host = FindAgentHost(frame_tree_node);
+  if (agent_host && agent_host->page_handler_) {

[nasko, 2016/07/13 22:37:34]

After offline chat with dgozman@, it became more clear to me that page_handler_
only exists for the main frame. This is definitely something that wasn't obvious
to me, so let's make sure we put a comment on this method.
Also, it makes the above comment obsolete and what is one thing that is common
across all navigations is the PageHadnler object.

[alex clarke (OOO till 29th), 2016/07/14 16:06:05]

Done.

+    return agent_host->page_handler_->GetThrottleForNavigation(
+        navigation_handle);
+  }
+  return nullptr;
+}
+
 RenderFrameDevToolsAgentHost::RenderFrameDevToolsAgentHost(
     RenderFrameHostImpl* host)
     : browser_handler_(new devtools::browser::BrowserHandler()),