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This CL move to the DFM 4 page totalling ~27.8 kB that are low-hanging
fruits because they already have their own GRD files.

Also taking the opportunity to reorganize:
* Move the pages' grit() targets to separate BUILD.gn files.
* Move chrome://invalidations resources to its own directory.


Bug: 927131
Change-Id: Ic31bd86e09312c8137661432788b2b58eade0bc5
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1949056Reviewed-by: Andrew Grieve <agrieve@chromium.org>
Reviewed-by: Dan Beam <dbeam@chromium.org>
Commit-Queue: Samuel Huang <huangs@chromium.org>
Cr-Commit-Position: refs/heads/master@{#721604}