Revert of Revert of Turn on clang by default on linux, 3rd try....

Revert of Revert of Turn on clang by default on linux, 3rd try. (https://codereview.chromium.org/378363006/)

Reason for revert:
This change should not have been reverted, since
it was easy to just disable these tests. thakis
explicitly requested "please ping thakis before
reverting it".

Original issue's description:
> Revert of Turn on clang by default on linux, 3rd try. (https://codereview.chromium.org/379413002/)
> 
> Reason for revert:
> NaClBrowserTestNonSfiMode.Messaging and NaClBrowserTestNonSfiMode.Irt failed.
> 
> http://build.chromium.org/p/chromium.linux/builders/Linux%20Tests/builds/12124/steps/browser_tests/logs/Irt
> http://build.chromium.org/p/chromium.linux/builders/Linux%20Tests/builds/12124/steps/browser_tests/logs/Messaging
> 
> Original issue's description:
> > Turn on clang by default on linux, 3rd try.
> > 
> > This is mostly to collect performance and size data for now, and to find out
> > if more bots need work. Unless things look really good, I'm going to revert
> > this by thursday morning (PDT).
> > 
> > BUG=360311
> > TBR=ajwong@chromium.org
> > 
> > Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=282246
> 
> TBR=awong@chromium.org,thakis@chromium.org
> NOTREECHECKS=true
> NOTRY=true
> BUG=360311
> 
> Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=282265

TBR=awong@chromium.org,thakis@chromium.org,horo@chromium.org
NOTREECHECKS=true
NOTRY=true
BUG=360311

Review URL: https://codereview.chromium.org/382743002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@282266 0039d316-1c4b-4281-b951-d872f2087c98

build/common.gypi

@@ -1777,6 +1777,10 @@
         # the class names, so the JNI generator needs to know this.
         'jni_generator_jarjar_file': '../android_webview/build/jarjar-rules.txt',
       }],
+      ['OS=="linux"', {
+        # TODO(thakis): This is here to measure perf for a while.
+        'clang%': 1,
+      }],  # OS=="mac"
       ['OS=="mac"', {
         'conditions': [
           # All Chrome builds have breakpad symbols, but only process the

tools/clang/scripts/update.sh

@@ -137,13 +137,6 @@ while [[ $# > 0 ]]; do
   shift
 done
 
-# Remove clang on bots where it was autoinstalled in r281914.
-if [[ -f "${LLVM_BUILD_DIR}/autoinstall_stamp" ]]; then
-  echo Removing autoinstalled clang and clobbering
-  rm -rf "${LLVM_BUILD_DIR}"
-  rm -rf "${THIS_DIR}/../../../out"
-fi
-
 if [[ -n "$if_needed" ]]; then
   if [[ "${OS}" == "Darwin" ]]; then
     # clang is used on Mac.
@@ -155,6 +148,12 @@ if [[ -n "$if_needed" ]]; then
     # clang previously downloaded, remove third_party/llvm-build to prevent
     # updating.
     true
+  elif [[ "${OS}" == "Linux" ]]; then
+    # Temporarily use clang on linux. Leave a stamp file behind, so that
+    # this script can remove clang again on machines where it was autoinstalled.
+    mkdir -p "${LLVM_BUILD_DIR}"
+    touch "${LLVM_BUILD_DIR}/autoinstall_stamp"
+    true
   else
     # clang wasn't needed, not doing anything.
     exit 0