[PA] Merge the partition_alloc_support files.

There are two partition_alloc_support file defined, one in content/ and
one in base/.

I would like to use the content/ one to enable BackupRefPtr and
DanglingPointerDetector in unittests. The problem: it will be used in
base/, which shouldn't depend on content/

This patch merged the two.

Bug: 1400059,1400058
Change-Id: I317c5694cb8cde793205ada7401882f79e93c065
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4110828
Reviewed-by: Bartek Nowierski <bartekn@chromium.org>
Auto-Submit: Arthur Sonzogni <arthursonzogni@chromium.org>
Commit-Queue: Bartek Nowierski <bartekn@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1084914}

base/allocator/partition_alloc_features.cc

@@ -157,6 +157,12 @@ const base::FeatureParam<AlternateBucketDistributionMode>
         AlternateBucketDistributionMode::kDefault,
         &kPartitionAllocAlternateDistributionOption};
 
+// Configures whether we set a lower limit for renderers that do not have a main
+// frame, similar to the limit that is already done for backgrounded renderers.
+BASE_FEATURE(kLowerPAMemoryLimitForNonMainRenderers,
+             "LowerPAMemoryLimitForNonMainRenderers",
+             FEATURE_DISABLED_BY_DEFAULT);
+
 // If enabled, switches PCScan scheduling to a mutator-aware scheduler. Does not
 // affect whether PCScan is enabled itself.
 BASE_FEATURE(kPartitionAllocPCScanMUAwareScheduler,

base/allocator/partition_alloc_features.h

@@ -115,6 +115,7 @@ extern const BASE_EXPORT base::FeatureParam<bool>
 extern const BASE_EXPORT base::FeatureParam<AlternateBucketDistributionMode>
     kPartitionAllocAlternateBucketDistributionParam;
 
+BASE_EXPORT BASE_DECLARE_FEATURE(kLowerPAMemoryLimitForNonMainRenderers);
 BASE_EXPORT BASE_DECLARE_FEATURE(kPartitionAllocPCScanMUAwareScheduler);
 BASE_EXPORT BASE_DECLARE_FEATURE(kPartitionAllocPCScanStackScanning);
 BASE_EXPORT BASE_DECLARE_FEATURE(kPartitionAllocDCScan);