Introduce ProcessRankPolicyAndroid

ProcessRankPolicyAndroid introduces the memory process priority concept
to Chrome on Android. This is to unblock introducing protected tab
concept to Chrome on Android which requires Performance Manager (e.g.
user edit information is only stored in PageNode out of Blink).

ProcessRankPolicyAndroid replaces TabImportanceManager.java which has
updated content::ChildProcessImportance via
WebContentsAndroid::SetImportance() which calls
RenderWidgetHostImpl::SetImportance().

ProcessRankPolicyAndroid contains the whole logic of
TabImportanceManager.java and visibility related conditions for main
frame in ChildProcessLauncherHelperImpl.setPriority().

* From TabImportanceManager:
  * Boosts the importance of the main frame of the focused tab to
    ChildProcessImportance::IMPORTANT with ChangeUnfocusedPriority.
  * Boosts the importance of the main frame of active tabs in invisible
    windows to ChildProcessImportance::MODERATE.
* From ChildProcessLauncherHelperImpl.setPriority():
  * Boosts the importance of the main frame of non-focused but visible
    tabs to ChildProcessImportance::IMPORTANT (if
    ChangeUnfocusedPriority is disabled) or
    ChildProcessImportance::MODERATE (if ChangeUnfocusedPriority is
    enabled)

ProcessRankPolicyAndroid does nothing to do with other frames in a page
other than the main frame. The priority of sub-frame processes are
updated by the existing logic in
ChildProcessLauncherHelperImpl.setPriority() which boosts sub-frames
with media stream and intersecting visible sub-frames.

Memory priority for sub-frames from Performance Manager will be done
later.

This also renames setImportance() method of WebContents.java
setPrimaryMainFrameImportance(). Historically the method had updated all
sub-frame importance, and https://crrev.com/c/1038759 changed it to
update the main frame only without renaming the java API.

DesignDocument: go/clank-memory-priority-policy

Bug: 401498479
Change-Id: I9046295757ed04a706ff9b9fe34f8b4f846ec81d
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6335184
Reviewed-by: Bo Liu <boliu@chromium.org>
Reviewed-by: Patrick Monette <pmonette@chromium.org>
Reviewed-by: David Trainor <dtrainor@chromium.org>
Reviewed-by: Alex Moshchuk <alexmos@chromium.org>
Commit-Queue: Shin Kawamura <kawasin@google.com>
Cr-Commit-Position: refs/heads/main@{#1445059}