This Cl fixes a fundamental misunderstanding when Wasm memory
histograms were added. They were added using
HISTOGRAM_MEMORY_LIST(). This macro implements aggregating memory
histograms that handle cases memory cases that are not module
specific.

The fixed memory histograms are all module specific, and are simple
histograms.

In addition, it removes field is_sync from ModuleCompiler and
WasmCompilationUnit, since the field is no longer needed to make the
fixed memory histograms synchronous.

Bug: v8:6361
Change-Id: I696109b4fd1a4aadc87a6bdbbc4b7daefd58ea51
Reviewed-on: https://chromium-review.googlesource.com/565349Reviewed-by: Brad Nelson <bradnelson@chromium.org>
Commit-Queue: Karl Schimpf <kschimpf@chromium.org>
Cr-Commit-Position: refs/heads/master@{#46541}