Add explicit includes of refcountedobject.h where it is used.

This is in preparation for deleting the include in rtc_base/refcount.h,
but that change has to wait for some downstream applications to 
not rely in the indirect include.

Partial reland of "Make rtc_base/refcount.h self contained, not including refcountedobject.h."

This is a reland of b7239a9dc825ddb25dbc800aed3a065163b9a10e
Original change's description:
> Make rtc_base/refcount.h self contained, not including refcountedobject.h.
> 
> The refcount.h file doesn't depend on anything from
> refcountedobject.h. The motivation of this change to make it possible
> to add additional declarations to refcount.h, and include it from
> refcountedobject.h.
> 
> Bug: webrtc:8270
> Change-Id: I24f6131f471e675570968d00065ff9b1f55e3373
> Reviewed-on: https://webrtc-review.googlesource.com/5760
> Reviewed-by: Karl Wiberg <kwiberg@webrtc.org>
> Commit-Queue: Niels Moller <nisse@webrtc.org>
> Cr-Commit-Position: refs/heads/master@{#20106}

Bug: webrtc:8270
Change-Id: I63a42712f6c1ec83823c629d1a954fd1a04d4a6c
Reviewed-on: https://webrtc-review.googlesource.com/7281
Commit-Queue: Karl Wiberg <kwiberg@webrtc.org>
Reviewed-by: Karl Wiberg <kwiberg@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#20185}
diff --git a/rtc_base/bind_unittest.cc b/rtc_base/bind_unittest.cc
index 7028ced..8703be4 100644
--- a/rtc_base/bind_unittest.cc
+++ b/rtc_base/bind_unittest.cc
@@ -14,6 +14,7 @@
 #include "rtc_base/gunit.h"
 
 #include "rtc_base/refcount.h"
+#include "rtc_base/refcountedobject.h"
 
 namespace rtc {
 
diff --git a/rtc_base/callback.h b/rtc_base/callback.h
index 1472b25..0e035ad 100644
--- a/rtc_base/callback.h
+++ b/rtc_base/callback.h
@@ -13,7 +13,7 @@
  */
 
 // To generate callback.h from callback.h.pump, execute:
-// /home/build/google3/third_party/gtest/scripts/pump.py callback.h.pump
+// ../third_party/googletest/src/googletest/scripts/pump.py callback.h.pump
 
 // Callbacks are callable object containers. They can hold a function pointer
 // or a function object and behave like a value type. Internally, data is
@@ -63,6 +63,7 @@
 #define RTC_BASE_CALLBACK_H_
 
 #include "rtc_base/refcount.h"
+#include "rtc_base/refcountedobject.h"
 #include "rtc_base/scoped_ref_ptr.h"
 
 namespace rtc {
diff --git a/rtc_base/callback.h.pump b/rtc_base/callback.h.pump
index 383fc19..2c40eab 100644
--- a/rtc_base/callback.h.pump
+++ b/rtc_base/callback.h.pump
@@ -9,7 +9,7 @@
  */
 
 // To generate callback.h from callback.h.pump, execute:
-// /home/build/google3/third_party/gtest/scripts/pump.py callback.h.pump
+// ../third_party/googletest/src/googletest/scripts/pump.py callback.h.pump
 
 // Callbacks are callable object containers. They can hold a function pointer
 // or a function object and behave like a value type. Internally, data is
@@ -58,6 +58,7 @@
 #define RTC_BASE_CALLBACK_H_
 
 #include "rtc_base/refcount.h"
+#include "rtc_base/refcountedobject.h"
 #include "rtc_base/scoped_ref_ptr.h"
 
 namespace rtc {
diff --git a/rtc_base/copyonwritebuffer.h b/rtc_base/copyonwritebuffer.h
index bdfe393..c4bba87 100644
--- a/rtc_base/copyonwritebuffer.h
+++ b/rtc_base/copyonwritebuffer.h
@@ -17,6 +17,7 @@
 #include "rtc_base/buffer.h"
 #include "rtc_base/checks.h"
 #include "rtc_base/refcount.h"
+#include "rtc_base/refcountedobject.h"
 #include "rtc_base/scoped_ref_ptr.h"
 
 namespace rtc {
diff --git a/rtc_base/refcount.h b/rtc_base/refcount.h
index a2664f0..6b49dec 100644
--- a/rtc_base/refcount.h
+++ b/rtc_base/refcount.h
@@ -10,6 +10,8 @@
 #ifndef RTC_BASE_REFCOUNT_H_
 #define RTC_BASE_REFCOUNT_H_
 
+// TODO(nisse): Delete this include. We plan to let refcountedobject.h
+// include this file, rather than the other way around.
 #include "rtc_base/refcountedobject.h"
 
 namespace rtc {
diff --git a/rtc_base/refcountedobject_unittest.cc b/rtc_base/refcountedobject_unittest.cc
index 688b921..143ca85 100644
--- a/rtc_base/refcountedobject_unittest.cc
+++ b/rtc_base/refcountedobject_unittest.cc
@@ -12,6 +12,7 @@
 
 #include "rtc_base/gunit.h"
 #include "rtc_base/refcount.h"
+#include "rtc_base/refcountedobject.h"
 
 namespace rtc {
 
diff --git a/rtc_base/rtccertificate.cc b/rtc_base/rtccertificate.cc
index 0c583b3..dd6f40a 100644
--- a/rtc_base/rtccertificate.cc
+++ b/rtc_base/rtccertificate.cc
@@ -13,6 +13,7 @@
 #include "rtc_base/rtccertificate.h"
 
 #include "rtc_base/checks.h"
+#include "rtc_base/refcountedobject.h"
 
 namespace rtc {
 
diff --git a/rtc_base/rtccertificategenerator.cc b/rtc_base/rtccertificategenerator.cc
index 1d99d10..cacff61 100644
--- a/rtc_base/rtccertificategenerator.cc
+++ b/rtc_base/rtccertificategenerator.cc
@@ -14,6 +14,7 @@
 #include <memory>
 
 #include "rtc_base/checks.h"
+#include "rtc_base/refcountedobject.h"
 #include "rtc_base/sslidentity.h"
 
 namespace rtc {
diff --git a/rtc_base/rtccertificategenerator_unittest.cc b/rtc_base/rtccertificategenerator_unittest.cc
index c8e1ab3..4ff6880 100644
--- a/rtc_base/rtccertificategenerator_unittest.cc
+++ b/rtc_base/rtccertificategenerator_unittest.cc
@@ -16,6 +16,7 @@
 #include "rtc_base/checks.h"
 #include "rtc_base/gunit.h"
 #include "rtc_base/logging.h"
+#include "rtc_base/refcountedobject.h"
 #include "rtc_base/thread.h"
 
 namespace rtc {
diff --git a/rtc_base/weak_ptr.h b/rtc_base/weak_ptr.h
index 7c1c15c..4950dfc 100644
--- a/rtc_base/weak_ptr.h
+++ b/rtc_base/weak_ptr.h
@@ -16,6 +16,7 @@
 #include <utility>
 
 #include "rtc_base/refcount.h"
+#include "rtc_base/refcountedobject.h"
 #include "rtc_base/scoped_ref_ptr.h"
 #include "rtc_base/sequenced_task_checker.h"