doc/go1.4.html: document new subrepo import paths

LGTM=r, adg
R=adg, r, 0xjnml, dr.volker.dobler
CC=golang-codereviews
https://golang.org/cl/166980044

doc/go1.4.html

@@ -120,7 +120,7 @@ compile but is easy to fix by adding an explicit dereference.
 <p>
 Go 1.4 can build binaries for ARM processors running the Android operating system.
 It can also build a <code>.so</code> library that can be loaded by an Android application
-using the supporting packages in the <a href="http://code.google.com/p/go.mobile">go.mobile</a> repository.
+using the supporting packages in the <a href="http://golang.org/x/mobile">mobile</a> subrepository.
 A brief description of the plans for this experimental port are available
 <a href="/s/go14android">here</a>.
 </p>
@@ -385,6 +385,24 @@ Further information is in
 <a href="http://golang.org/s/go14customimport">the design document</a>.
 </p>
 
+<h3 id="subrepo">Import paths for the subrepositories</h3>
+
+<p>
+The Go project subrepositories (<code>code.google.com/p/go.tools</code> and so on)
+are now available under custom import paths replacing <code>code.google.com/p/go.</code> with <code>golang.org/x/</code>,
+as in <code>golang.org/x/tools</code>.
+We will add canonical import comments to the code around June 1, 2015,
+at which point Go 1.4 and later will stop accepting the old <code>code.google.com</code> paths.
+</p>
+
+<p>
+<em>Updating</em>: All code that imports from subrepositories should change
+to use the new <code>golang.org</code> paths.
+Go 1.0 and later can resolve and import the new paths, so updating will not break
+compatibility with older releases.
+Code that has not updated will stop compiling with Go 1.4 around June 1, 2015.
+</p>
+
 <h3 id="gogenerate">The go generate subcommand</h3>
 
 <p>
@@ -394,8 +412,8 @@ to automate the running of tools to generate source code before compilation.
 For example, it can be used to run the <a href="/cmd/yacc"><code>yacc</code></a>
 compiler-compiler on a <code>.y</code> file to produce the Go source file implementing the grammar,
 or to automate the generation of <code>String</code> methods for typed constants using the new
-<a href="http://godoc.org/code.google.com/p/go.tools/cmd/stringer">stringer</a>
-tool in the <code>go.tools</code> repository.
+<a href="http://godoc.org/golang.org/x/tools/cmd/stringer">stringer</a>
+tool in the <code>golang.org/x/tools</code> subrepository.
 </p>
 
 <p>
@@ -480,7 +498,7 @@ rebuild the standard library and commands, to avoid overwriting the installation
 <p>
 In the main Go source repository, the source code for the packages was kept in
 the directory <code>src/pkg</code>, which made sense but differed from
-other repositories, including the Go sub-repositories such as <code>go.tools</code>.
+other repositories, including the Go subrepositories.
 In Go 1.4, the<code> pkg</code> level of the source tree is now gone, so for example
 the <a href="/pkg/fmt/"><code>fmt</code></a> package's source, once kept in
 directory <code>src/pkg/fmt</code>, now lives one level higher in <code>src/fmt</code>.
@@ -591,14 +609,14 @@ separate document</a>.
 </p>
 
 <p>
-A new subrepository, <a href="http://code.google.com/p/go.sys">go.sys</a>,
+A new subrepository, <a href="http://golang.org/x/sys">golang.org/x/sys</a>,
 has been created to serve as the location for new developments to support system
 calls on all kernels.
 It has a nicer structure, with three packages that each hold the implementation of
 system calls for one of
-<a href="http://godoc.org/code.google.com/p/go.sys/unix">Unix</a>,
-<a href="http://godoc.org/code.google.com/p/go.sys/windows">Windows</a> and
-<a href="http://godoc.org/code.google.com/p/go.sys/plan9">Plan 9</a>.
+<a href="http://godoc.org/golang.org/x/sys/unix">Unix</a>,
+<a href="http://godoc.org/golang.org/x/sys/windows">Windows</a> and
+<a href="http://godoc.org/golang.org/x/sys/plan9">Plan 9</a>.
 These packages will be curated more generously, accepting all reasonable changes
 that reflect kernel interfaces in those operating systems.
 See the documentation and the article mentioned above for more information.
@@ -608,7 +626,7 @@ See the documentation and the article mentioned above for more information.
 <em>Updating</em>: Existing programs are not affected as the <code>syscall</code>
 package is largely unchanged from the 1.3 release.
 Future development that requires system calls not in the <code>syscall</code> package
-should build on <code>go.sys</code> instead.
+should build on <code>golang.org/x/sys</code> instead.
 </p>
 
 <h3 id="minor_library_changes">Minor changes to the library</h3>