Enable jumbo for media/cast

Building //media takes around 23 CPU minutes. A experimental
branch showed that this could be reduced, by using jumbo,
to around 9 CPU minutes. media/cast is the fourth largest part
of media and takes around 2 CPU minutes to compile without
jumbo.

This commit enables jumbo for media/cast.

Bug: 867350
Change-Id: Iaefb6e7ac95c1c7fab78478f879a8ba542f329d9
Reviewed-on: https://chromium-review.googlesource.com/1152807Reviewed-by: Chrome Cunningham (In Paris) <chcunningham@chromium.org>
Commit-Queue: Chrome Cunningham (In Paris) <chcunningham@chromium.org>
Cr-Commit-Position: refs/heads/master@{#578609}

media/cast/BUILD.gn

@@ -4,6 +4,7 @@
 
 import("//build/config/android/config.gni")
 import("//build/config/features.gni")
+import("//build/config/jumbo.gni")
 import("//build/config/ui.gni")
 import("//testing/test.gni")
 import("//third_party/protobuf/proto_library.gni")
@@ -15,7 +16,7 @@ proto_library("logging_proto") {
 }
 
 # Common code shared by all cast components.
-source_set("common") {
+jumbo_source_set("common") {
   sources = [
     "cast_config.cc",
     "cast_config.h",
@@ -70,7 +71,7 @@ source_set("common") {
   ]
 }
 
-source_set("net") {
+jumbo_source_set("net") {
   sources = [
     "net/cast_transport.h",
     "net/cast_transport_config.cc",
@@ -124,7 +125,7 @@ source_set("net") {
   ]
 }
 
-source_set("sender") {
+jumbo_source_set("sender") {
   sources = [
     "cast_sender.h",
     "cast_sender_impl.cc",
@@ -189,7 +190,7 @@ source_set("sender") {
   }
 }
 
-source_set("receiver") {
+jumbo_source_set("receiver") {
   sources = [
     "cast_receiver.h",
     "net/rtp/cast_message_builder.cc",