Fix documentation for Android code coverage generation.

The instructions seem to assume running the script from /src and
the intent is to create two directories

/tmp/coverage
/tmp/coverage_report

but the lack of a slash prefix results in the creation of...

/tmp/coverage
/src/tmp/coverage_report

Bug: None
Change-Id: Ib10050a577fc8e9494a903386d5886ccbef8aa1e
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2124256
Commit-Queue: John Budorick <[email protected]>
Reviewed-by: Yun Liu <[email protected]>
Reviewed-by: John Budorick <[email protected]>
Cr-Commit-Position: refs/heads/master@{#754026}
diff --git a/build/android/docs/coverage.md b/build/android/docs/coverage.md
index 35cd809..17c83c6 100644
--- a/build/android/docs/coverage.md
+++ b/build/android/docs/coverage.md
@@ -37,7 +37,7 @@
   ```shell
   build/android/generate_jacoco_report.py \
      --format html \
-     --output-dir tmp/coverage_report/ \
+     --output-dir /tmp/coverage_report/ \
      --coverage-dir /tmp/coverage/ \
      --sources-json-dir out/Debug/ \
   ```
@@ -57,7 +57,7 @@
   ```shell
   build/android/generate_jacoco_report.py \
     --format xml \
-    --output-file tmp/coverage_report/report.xml \
+    --output-file /tmp/coverage_report/report.xml \
     --coverage-dir /tmp/coverage/ \
     --sources-json-dir out/Debug/ \
   ```
@@ -67,7 +67,7 @@
   ```shell
   build/android/generate_jacoco_report.py \
     --format csv \
-    --output-file tmp/coverage_report/report.csv \
+    --output-file /tmp/coverage_report/report.csv \
     --coverage-dir /tmp/coverage/ \
     --sources-json-dir out/Debug/ \
   ```