make allocPixels throw on failure

BUG=skia:
R=mtklein@google.com, fmalita@google.com, fmalita@chromium.org

Author: reed@google.com

Review URL: https://codereview.chromium.org/510423005
diff --git a/tests/WritePixelsTest.cpp b/tests/WritePixelsTest.cpp
index 2a8d059..f47c67b 100644
--- a/tests/WritePixelsTest.cpp
+++ b/tests/WritePixelsTest.cpp
@@ -115,8 +115,7 @@
 static void fillCanvas(SkCanvas* canvas) {
     SkBitmap bmp;
     if (bmp.isNull()) {
-        SkDEBUGCODE(bool alloc = ) bmp.allocN32Pixels(DEV_W, DEV_H);
-        SkASSERT(alloc);
+        bmp.allocN32Pixels(DEV_W, DEV_H);
         for (int y = 0; y < DEV_H; ++y) {
             for (int x = 0; x < DEV_W; ++x) {
                 *bmp.getAddr32(x, y) = getCanvasColor(x, y);