Set is_multi_dll_chrome to false by default

This change sets is_multi_dll_chrome to false by default thus merging
chrome.dll and chrome_child.dll to a single dll.  This saves disk space
and improves startup performance.  It is also consistent with all other
platforms (windows was the only platform the split was enabled by
default).

Bug: 726150
Change-Id: Iade2c7f1bbe696d45ebac7483072f7e2e7e84ab4
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1850272Reviewed-by: Bruce Dawson <brucedawson@chromium.org>
Reviewed-by: Will Harris <wfh@chromium.org>
Reviewed-by: Nico Weber <thakis@chromium.org>
Commit-Queue: Nico Weber <thakis@chromium.org>
Cr-Commit-Position: refs/heads/master@{#705667}

build/config/chrome_build.gni

@@ -10,7 +10,8 @@ declare_args() {
 
   # Break chrome.dll into multple pieces based on process type. Only available
   # on Windows.
-  is_multi_dll_chrome = is_win && !is_component_build
+  # TODO: Remove this flag once m79 has shipped with this disabled.
+  is_multi_dll_chrome = false
 
   # Turn this on to generate order files. See
   # https://chromium.googlesource.com/chromium/src/+/master/docs/win_order_files.md