split MEMORY_TOOL_REPLACES_ALLOCATOR into initial size and malloc.

currently all sanitizer use MEMORY_TOOL_REPLACES_ALLOCATOR defines
for setting initial size and malloc allocation.
However none memory sanitizer tools like deep-memory-profiler 
doesn't need to set initial size.
This is a patch for splitting the define up into
MEMORY_TOOL_REPLACES_ALLOCATOR, MEMORY_SANITIZER_INITIAL_SIZE.

BUG=None

Review URL: https://codereview.chromium.org/357603002

git-svn-id: svn://svn.chromium.org/blink/trunk@177521 bbb929c8-8fbe-4397-9dbb-9b2b20218538