[LPM] Speculative fix for Mac builds of skia proto fuzzer.

On Mac builds, it looks like calling WriteNum on a size_t was causing
the compiler to select the templated version of WriteNum rather than the
uint64_t version. Hopefully it won't do the opposite (and break on calls
to WriteNum(uint64_t) because of this fix.

Bug: 808155, 769578
Change-Id: I8babcf6da5090b9bffdbcc98b573c11c02f2e489
Reviewed-on: https://chromium-review.googlesource.com/899906
Commit-Queue: Jonathan Metzman <metzman@chromium.org>
Reviewed-by: Martin Barbella <mbarbella@chromium.org>
Cr-Commit-Position: refs/heads/master@{#534143}

testing/libfuzzer/proto/skia_image_filter_proto_converter.cc

@@ -757,18 +757,21 @@ size_t Converter::PopStartSize() {
 
 template <typename T>
 void Converter::WriteNum(const T num) {
-  CHECK_LE(sizeof(T), static_cast<size_t>(4));
+  if (sizeof(T) > 4) {
+    CHECK(num <= UINT32_MAX);
+    uint32_t four_byte_num = static_cast<uint32_t>(num);
+    char num_arr[sizeof(four_byte_num)];
+    memcpy(num_arr, &four_byte_num, sizeof(four_byte_num));
+    for (size_t idx = 0; idx < sizeof(four_byte_num); idx++)
+      output_.push_back(num_arr[idx]);
+    return;
+  }
   char num_arr[sizeof(T)];
   memcpy(num_arr, &num, sizeof(T));
   for (size_t idx = 0; idx < sizeof(T); idx++)
     output_.push_back(num_arr[idx]);
 }
 
-void Converter::WriteNum(const uint64_t num) {
-  CHECK_LE(num, UINT32_MAX);
-  WriteNum(static_cast<uint32_t>(num));
-}
-
 void Converter::InsertSize(const size_t size, const uint32_t position) {
   char size_arr[sizeof(uint32_t)];
   memcpy(size_arr, &size, sizeof(uint32_t));

testing/libfuzzer/proto/skia_image_filter_proto_converter.h

@@ -340,7 +340,6 @@ class Converter {
   template <typename T>
   void WriteUInt8(T num);
   void WriteUInt16(uint16_t num);
-  void WriteNum(const uint64_t num);
   void WriteNum(const char (&num_arr)[4]);
   // Write num as a number. Assumes num is four bytes or less.
   template <class T>