go.image: use golang.org/x/... import paths

LGTM=bradfitz, rsc
R=rsc, bradfitz
CC=golang-codereviews
https://golang.org/cl/169090043

 cmd/webp-manual-test/main.go | 4 ++--
 riff/example_test.go         | 2 +-
 tiff/reader.go               | 2 +-
 webp/decode.go               | 8 ++++----
 webp/decode_test.go          | 2 +-
 5 files changed, 9 insertions(+), 9 deletions(-)

diff --git a/cmd/webp-manual-test/main.go b/cmd/webp-manual-test/main.go
index 3d17734..92c27e1 100644
--- a/cmd/webp-manual-test/main.go
+++ b/cmd/webp-manual-test/main.go
@@ -16,8 +16,8 @@ import (
 	"sort"
 	"strings"
 
-	"code.google.com/p/go.image/webp"
-	"code.google.com/p/go.image/webp/nycbcra"
+	"golang.org/x/image/webp"
+	"golang.org/x/image/webp/nycbcra"
 )
 
 var (
diff --git a/riff/example_test.go b/riff/example_test.go
index faa4975..93c72b0 100644
--- a/riff/example_test.go
+++ b/riff/example_test.go
@@ -11,7 +11,7 @@ import (
 	"log"
 	"strings"
 
-	"code.google.com/p/go.image/riff"
+	"golang.org/x/image/riff"
 )
 
 func ExampleReader() {
diff --git a/tiff/reader.go b/tiff/reader.go
index f4ccd23..929ef04 100644
--- a/tiff/reader.go
+++ b/tiff/reader.go
@@ -16,7 +16,7 @@ import (
 	"io"
 	"io/ioutil"
 
-	"code.google.com/p/go.image/tiff/lzw"
+	"golang.org/x/image/tiff/lzw"
 )
 
 // A FormatError reports that the input is not a valid TIFF image.
diff --git a/webp/decode.go b/webp/decode.go
index faf9ebf..527a7ea 100644
--- a/webp/decode.go
+++ b/webp/decode.go
@@ -15,10 +15,10 @@ import (
 	"image/color"
 	"io"
 
-	"code.google.com/p/go.image/riff"
-	"code.google.com/p/go.image/vp8"
-	"code.google.com/p/go.image/vp8l"
-	"code.google.com/p/go.image/webp/nycbcra"
+	"golang.org/x/image/riff"
+	"golang.org/x/image/vp8"
+	"golang.org/x/image/vp8l"
+	"golang.org/x/image/webp/nycbcra"
 )
 
 var errInvalidFormat = errors.New("webp: invalid format")
diff --git a/webp/decode_test.go b/webp/decode_test.go
index b1af0e7..581d29e 100644
--- a/webp/decode_test.go
+++ b/webp/decode_test.go
@@ -14,7 +14,7 @@ import (
 	"strings"
 	"testing"
 
-	"code.google.com/p/go.image/webp/nycbcra"
+	"golang.org/x/image/webp/nycbcra"
 )
 
 // hex is like fmt.Sprintf("% x", x) but also inserts dots every 16 bytes, to