Remove internal media/base/ stringstream usages

The %f -> %g changes are there to make the SimpleStringBuilder behave like stringstream/cout and friends. With %f it prints e.g. 2.2 as 2.200000. This change also makes it use scientific notation for numbers > 1000000, like the other streams.

Bug: webrtc:8982
Change-Id: Id174b02c5776460607f48efc196a08673b67eeb0
Reviewed-on: https://webrtc-review.googlesource.com/67080
Commit-Queue: Jonas Olsson <jonasolsson@webrtc.org>
Reviewed-by: Karl Wiberg <kwiberg@webrtc.org>
Reviewed-by: Fredrik Solenberg <solenberg@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#23094}
diff --git a/rtc_base/strings/string_builder_unittest.cc b/rtc_base/strings/string_builder_unittest.cc
index 8d6312f..aa570eb 100644
--- a/rtc_base/strings/string_builder_unittest.cc
+++ b/rtc_base/strings/string_builder_unittest.cc
@@ -33,7 +33,7 @@
   SimpleStringBuilder sb(sb_buf);
   sb << 1 << ':' << 2.1 << ":" << 2.2f << ':' << 78187493520ll << ':'
      << 78187493520ul;
-  EXPECT_EQ(0, strcmp(sb.str(), "1:2.100000:2.200000:78187493520:78187493520"));
+  EXPECT_EQ(0, strcmp(sb.str(), "1:2.1:2.2:78187493520:78187493520"));
 }
 
 TEST(SimpleStringBuilder, Format) {