add installPixels

BUG=skia:
R=halcanary@google.com

Review URL: https://codereview.chromium.org/143073008

git-svn-id: http://skia.googlecode.com/svn/trunk@13174 2bbb7eff-a529-9590-31e7-b0007b416f81
diff --git a/src/effects/SkDisplacementMapEffect.cpp b/src/effects/SkDisplacementMapEffect.cpp
index 8264ec8..6ad46ba 100644
--- a/src/effects/SkDisplacementMapEffect.cpp
+++ b/src/effects/SkDisplacementMapEffect.cpp
@@ -229,8 +229,7 @@
     }
 
     dst->setConfig(color.config(), bounds.width(), bounds.height());
-    dst->allocPixels();
-    if (!dst->getPixels()) {
+    if (!dst->allocPixels()) {
         return false;
     }