Normalize dex compression ratio in normalized_apk_size

This was causing some changes that reduce size to show as increasing
normalized size (and vice versa).

Binary-Size: Metrics change
Bug: 979205
Change-Id: I90219b7cf454f91dc64474c07caaf0ca0edcbf13
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1811517
Commit-Queue: Andrew Grieve <agrieve@chromium.org>
Reviewed-by: Eric Stevenson <estevenson@chromium.org>
Cr-Commit-Position: refs/heads/master@{#697770}

build/android/resource_sizes.py

@@ -441,6 +441,11 @@ def _DoApkAnalysis(apk_filename, apks_path, tool_prefix, out_dir, report_func):
   # file size. Also gets rid of compression.
   normalized_apk_size -= native_code.ComputeZippedSize()
   normalized_apk_size += native_code_unaligned_size
+  # Normalized dex size: Size within the zip + size on disk for Android Go
+  # devices running Android O (which ~= uncompressed dex size).
+  # Use a constant compression factor to account for fluctuations.
+  normalized_apk_size -= java_code.ComputeZippedSize()
+  normalized_apk_size += int(java_code.ComputeUncompressedSize() * 1.5)
   # Unaligned size should be ~= uncompressed size or something is wrong.
   # As of now, padding_fraction ~= .007
   padding_fraction = -_PercentageDifference(
@@ -450,9 +455,6 @@ def _DoApkAnalysis(apk_filename, apks_path, tool_prefix, out_dir, report_func):
           padding_fraction, native_code.ComputeUncompressedSize(),
           native_code_unaligned_size))
 
-  # Normalized dex size: size within the zip + size on disk for Android Go
-  # devices (which ~= uncompressed dex size).
-  normalized_apk_size += java_code.ComputeUncompressedSize()
   if apks_path:
     # Locale normalization not needed when measuring only one locale.
     # E.g. a change that adds 300 chars of unstranslated strings would cause the

docs/speed/binary_size/metrics.md

@@ -37,9 +37,10 @@ For Googlers, more information available at [go/chrome-apk-size](https://goto.go
  * Computed as:
    * The size of an APK
    * With all native code as the sum of section sizes (except .bss), uncompressed.
-   * With all dex code as if it were stored compressed and also extracted.
+   * With all dex code counted as `uncompressed_size * 1.5` (meant to simulate Android Go on Oreo).
    * With all translations as if they were not missing (estimates size of missing translations based on size of english strings).
      * Without translation-normalization, translation dumps cause jumps.
+     * Translation-normalization applies only to apks (not to Android App Bundles).
 
 ### Native Code Size Metrics