Moving HTTP POST body from StartNavigationParams to CommonNavigationParams.

StartNavigationParams used to hold
    std::vector<unsigned char> browser_initiated_post_data
field.  This CL moves the field to CommonNavigationParams and makes it
more generic, so that it can be used to carry any POST data (nost just
"browser initiated" post data):
    scoped_refptr<ResourceRequestBody> post_data;

Making the type more generic (i.e. replacing a vector of bytes with
ResourceRequestBody) is needed to prepare for forwarding POST data back to the
renderer during process transfers.  This fix will come in crrev.com/1956383003.

Moving the type from StartNavigationParams to CommonNavigationParams helps
unify many scenarios across default and PlzNavigate modes and consequently
allows avoiding passing of the body as a separate field and/or param in
quite a few places.

BUG=582211
CQ_INCLUDE_TRYBOTS=tryserver.chromium.linux:linux_site_isolation

Review-Url: https://codereview.chromium.org/1999943002
Cr-Commit-Position: refs/heads/master@{#395915}
diff --git a/content/browser/frame_host/navigator_impl.h b/content/browser/frame_host/navigator_impl.h
index 14958713..d760f7c 100644
--- a/content/browser/frame_host/navigator_impl.h
+++ b/content/browser/frame_host/navigator_impl.h
@@ -80,8 +80,7 @@
   void OnBeforeUnloadACK(FrameTreeNode* frame_tree_node, bool proceed) override;
   void OnBeginNavigation(FrameTreeNode* frame_tree_node,
                          const CommonNavigationParams& common_params,
-                         const BeginNavigationParams& begin_params,
-                         scoped_refptr<ResourceRequestBody> body) override;
+                         const BeginNavigationParams& begin_params) override;
   void FailedNavigation(FrameTreeNode* frame_tree_node,
                         bool has_stale_copy_in_cache,
                         int error_code) override;