Force memcpy when reading a float, to avoid alignment issues

Despite our best efforts to align data when writing, when reading the data may
not be sufficiently aligned, causing some ARM platforms to SIGBUS when reading
floats. Force a memcpy instead to sidestep the issue.

BUG=315213

Review URL: https://codereview.chromium.org/73333002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@235590 0039d316-1c4b-4281-b951-d872f2087c98

base/pickle.cc

@@ -91,7 +91,15 @@ bool PickleIterator::ReadUInt64(uint64* result) {
 }
 
 bool PickleIterator::ReadFloat(float* result) {
-  return ReadBuiltinType(result);
+  // crbug.com/315213
+  // The source data may not be properly aligned, and unaligned float reads
+  // cause SIGBUS on some ARM platforms, so force using memcpy to copy the data
+  // into the result.
+  const char* read_from = GetReadPointerAndAdvance<float>();
+  if (!read_from)
+    return false;
+  memcpy(result, read_from, sizeof(*result));
+  return true;
 }
 
 bool PickleIterator::ReadString(std::string* result) {