add realloc method to SkAutoSTMalloc

BUG=skia:

Review URL: https://codereview.chromium.org/1069013002

gyp/tests.gypi

@@ -216,6 +216,7 @@
     '../tests/SVGDeviceTest.cpp',
     '../tests/TessellatingPathRendererTests.cpp',
     '../tests/TArrayTest.cpp',
+    '../tests/TemplatesTest.cpp',
     '../tests/TDPQueueTest.cpp',
     '../tests/Time.cpp',
     '../tests/TLSTest.cpp',

include/core/SkTemplates.h

@@ -411,17 +411,13 @@ private:
 
 template <size_t N, typename T> class SkAutoSTMalloc : SkNoncopyable {
 public:
-    SkAutoSTMalloc() {
-        fPtr = NULL;
-    }
+    SkAutoSTMalloc() : fPtr(fTStorage) {}
 
     SkAutoSTMalloc(size_t count) {
         if (count > N) {
             fPtr = (T*)sk_malloc_flags(count * sizeof(T), SK_MALLOC_THROW | SK_MALLOC_TEMP);
-        } else if (count) {
-            fPtr = fTStorage;
         } else {
-            fPtr = NULL;
+            fPtr = fTStorage;
         }
     }
 
@@ -437,11 +433,9 @@ public:
             sk_free(fPtr);
         }
         if (count > N) {
-            fPtr = (T*)sk_malloc_flags(count * sizeof(T), SK_MALLOC_THROW | SK_MALLOC_TEMP);
-        } else if (count) {
-            fPtr = fTStorage;
+            fPtr = (T*)sk_malloc_throw(count * sizeof(T));
         } else {
-            fPtr = NULL;
+            fPtr = fTStorage;
         }
         return fPtr;
     }
@@ -464,6 +458,20 @@ public:
         return fPtr[index];
     }
 
+    // Reallocs the array, can be used to shrink the allocation.  Makes no attempt to be intelligent
+    void realloc(size_t count) {
+        if (count > N) {
+            if (fPtr == fTStorage) {
+                fPtr = (T*)sk_malloc_throw(count * sizeof(T));
+                memcpy(fPtr, fTStorage, N * sizeof(T));
+            } else {
+                fPtr = (T*)sk_realloc_throw(fPtr, count * sizeof(T));
+            }
+        } else if (fPtr != fTStorage) {
+            fPtr = (T*)sk_realloc_throw(fPtr, count * sizeof(T));
+        }
+    }
+
 private:
     T*          fPtr;
     union {

tests/TemplatesTest.cpp

@@ -0,0 +1,72 @@
+/*
+ * Copyright 2015 Google Inc.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+#include "SkTemplates.h"
+#include "Test.h"
+
+// Tests for some of the helpers in SkTemplates.h
+static void test_automalloc_realloc(skiatest::Reporter* reporter) {
+    SkAutoSTMalloc<1, int> array;
+
+    // test we have a valid pointer, should not crash
+    array[0] = 1;
+    REPORTER_ASSERT(reporter, array[0] == 1);
+
+    // using realloc for init
+    array.realloc(1);
+
+    array[0] = 1;
+    REPORTER_ASSERT(reporter, array[0] == 1);
+
+    // verify realloc can grow
+    array.realloc(2);
+    REPORTER_ASSERT(reporter, array[0] == 1);
+
+    // realloc can shrink
+    array.realloc(1);
+    REPORTER_ASSERT(reporter, array[0] == 1);
+
+    // should not crash
+    array.realloc(0);
+
+    // grow and shrink again
+    array.realloc(10);
+    for (int i = 0; i < 10; i++) {
+        array[i] = 10 - i;
+    }
+    array.realloc(20);
+    for (int i = 0; i < 10; i++) {
+        REPORTER_ASSERT(reporter, array[i] == 10 - i);
+    }
+    array.realloc(10);
+    for (int i = 0; i < 10; i++) {
+        REPORTER_ASSERT(reporter, array[i] == 10 - i);
+    }
+
+    array.realloc(1);
+    REPORTER_ASSERT(reporter, array[0] = 10);
+
+    // resets mixed with realloc, below stack alloc size
+    array.reset(0);
+    array.realloc(1);
+    array.reset(1);
+
+    array[0] = 1;
+    REPORTER_ASSERT(reporter, array[0] == 1);
+
+    // reset and realloc > stack size
+    array.reset(2);
+    array.realloc(3);
+    array[0] = 1;
+    REPORTER_ASSERT(reporter, array[0] == 1);
+    array.realloc(1);
+    REPORTER_ASSERT(reporter, array[0] == 1);
+}
+
+DEF_TEST(Templates, reporter) {
+    test_automalloc_realloc(reporter);
+}