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/ARGBImageEncoderTest.cpp b/tests/ARGBImageEncoderTest.cpp
index 18f315f..4d16f4c 100644
--- a/tests/ARGBImageEncoderTest.cpp
+++ b/tests/ARGBImageEncoderTest.cpp
@@ -35,9 +35,8 @@
         // A bitmap that should generate the above bytes:
         SkBitmap bitmap;
         {
-            bool success = bitmap.allocPixels(SkImageInfo::Make(kWidth, kHeight,
-                                                        gColorTypes[ctIndex], kOpaque_SkAlphaType));
-            REPORTER_ASSERT(reporter, success);
+            bitmap.allocPixels(SkImageInfo::Make(kWidth, kHeight, gColorTypes[ctIndex],
+                                                 kOpaque_SkAlphaType));
             bitmap.eraseColor(SK_ColorBLUE);
             // Change rows [0,1] from blue to [red,green].
             SkCanvas canvas(bitmap);